diff --git a/src/ConvertKit_API.php b/src/ConvertKit_API.php
index 6c5e6eb..86b1888 100644
--- a/src/ConvertKit_API.php
+++ b/src/ConvertKit_API.php
@@ -18,6 +18,8 @@
  */
 class ConvertKit_API
 {
+    use ConvertKit_API_Traits;
+
     /**
      * The SDK version.
      *
@@ -25,55 +27,6 @@ class ConvertKit_API
      */
     public const VERSION = '2.0.0';
 
-    /**
-     * ConvertKit OAuth Application Client ID
-     *
-     * @var string
-     */
-    protected $client_id = '';
-
-    /**
-     * ConvertKit OAuth Application Client Secret
-     *
-     * @var string
-     */
-    protected $client_secret = '';
-
-    /**
-     * Access Token
-     *
-     * @var string
-     */
-    protected $access_token = '';
-
-    /**
-     * OAuth Authorization URL
-     *
-     * @var string
-     */
-    protected $oauth_authorize_url = 'https://app.convertkit.com/oauth/authorize';
-
-    /**
-     * OAuth Token URL
-     *
-     * @var string
-     */
-    protected $oauth_token_url = 'https://api.convertkit.com/oauth/token';
-
-    /**
-     * Version of ConvertKit API
-     *
-     * @var string
-     */
-    protected $api_version = 'v4';
-
-    /**
-     * ConvertKit API URL
-     *
-     * @var string
-     */
-    protected $api_url_base = 'https://api.convertkit.com/';
-
     /**
      * Debug
      *
@@ -231,7 +184,7 @@ public function get_access_token(string $authCode, string $redirectURI)
         $request = new Request(
             method: 'POST',
             uri:    $this->oauth_token_url,
-            headers: $this->request_headers(
+            headers: $this->get_request_headers(
                 auth: false
             ),
             body:   (string) json_encode(
@@ -269,7 +222,7 @@ public function refresh_token(string $refreshToken, string $redirectURI)
         $request = new Request(
             method: 'POST',
             uri: $this->oauth_token_url,
-            headers: $this->request_headers(
+            headers: $this->get_request_headers(
                 auth: false
             ),
             body: (string) json_encode(
@@ -294,1881 +247,202 @@ public function refresh_token(string $refreshToken, string $redirectURI)
     }
 
     /**
-     * Gets the current account
-     *
-     * @see https://developers.convertkit.com/v4.html#get-current-account
-     *
-     * @return false|mixed
-     */
-    public function get_account()
-    {
-        return $this->get('account');
-    }
-
-    /**
-     * Gets the account's colors
+     * Get markup from ConvertKit for the provided $url.
      *
-     * @see https://developers.convertkit.com/v4.html#list-colors
+     * Supports legacy forms and legacy landing pages.
      *
-     * @return false|mixed
-     */
-    public function get_account_colors()
-    {
-        return $this->get('account/colors');
-    }
-
-    /**
-     * Gets the account's colors
+     * Forms and Landing Pages should be embedded using the supplied JS embed script in
+     * the API response when using get_forms() or get_landing_pages().
      *
-     * @param array<string, string> $colors Hex colors.
+     * @param string $url URL of HTML page.
      *
-     * @see https://developers.convertkit.com/v4.html#list-colors
+     * @throws \InvalidArgumentException If the URL is not a valid URL format.
+     * @throws \Exception If parsing the legacy form or landing page failed.
      *
-     * @return false|mixed
+     * @return false|string
      */
-    public function update_account_colors(array $colors)
+    public function get_resource(string $url)
     {
-        return $this->put(
-            endpoint: 'account/colors',
-            args: ['colors' => $colors]
-        );
-    }
+        if (!filter_var($url, FILTER_VALIDATE_URL)) {
+            throw new \InvalidArgumentException();
+        }
 
-    /**
-     * Gets the Creator Profile
-     *
-     * @see https://developers.convertkit.com/v4.html#get-creator-profile
-     *
-     * @return false|mixed
-     */
-    public function get_creator_profile()
-    {
-        return $this->get('account/creator_profile');
-    }
+        $resource = '';
 
-    /**
-     * Gets email stats
-     *
-     * @see https://developers.convertkit.com/v4.html#get-email-stats
-     *
-     * @return false|mixed
-     */
-    public function get_email_stats()
-    {
-        return $this->get('account/email_stats');
-    }
+        $this->create_log(sprintf('Getting resource %s', $url));
 
-    /**
-     * Gets growth stats
-     *
-     * @param \DateTime $starting Gets stats for time period beginning on this date. Defaults to 90 days ago.
-     * @param \DateTime $ending   Gets stats for time period ending on this date. Defaults to today.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-growth-stats
-     *
-     * @return false|mixed
-     */
-    public function get_growth_stats(\DateTime $starting = null, \DateTime $ending = null)
-    {
-        return $this->get(
-            'account/growth_stats',
-            [
-                'starting' => (!is_null($starting) ? $starting->format('Y-m-d') : ''),
-                'ending'   => (!is_null($ending) ? $ending->format('Y-m-d') : ''),
-            ]
+        // Fetch the resource.
+        $request  = new Request(
+            method: 'GET',
+            uri: $url,
+            headers: $this->get_request_headers(
+                type: 'text/html',
+                auth: false
+            ),
         );
-    }
+        $response = $this->client->send($request);
 
-    /**
-     * Get forms.
-     *
-     * @param string  $status              Form status (active|archived|trashed|all).
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
-     *
-     * @return false|array<int,\stdClass>
-     */
-    public function get_forms(
-        string $status = 'active',
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        return $this->get(
-            endpoint: 'forms',
-            args: $this->build_total_count_and_pagination_params(
-                params: [
-                    'type'   => 'embed',
-                    'status' => $status,
-                ],
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
+        // Fetch HTML.
+        $body = $response->getBody()->getContents();
 
-    /**
-     * Get landing pages.
-     *
-     * @param string  $status              Form status (active|archived|trashed|all).
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
-     *
-     * @return false|array<int,\stdClass>
-     */
-    public function get_landing_pages(
-        string $status = 'active',
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        return $this->get(
-            endpoint: 'forms',
-            args: $this->build_total_count_and_pagination_params(
-                params: [
-                    'type'   => 'hosted',
-                    'status' => $status,
-                ],
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
+        // Forcibly tell DOMDocument that this HTML uses the UTF-8 charset.
+        // <meta charset="utf-8"> isn't enough, as DOMDocument still interprets the HTML as ISO-8859,
+        // which breaks character encoding.
+        // Use of mb_convert_encoding() with HTML-ENTITIES is deprecated in PHP 8.2, so we have to use this method.
+        // If we don't, special characters render incorrectly.
+        $body = str_replace(
+            '<head>',
+            '<head>' . "\n" . '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">',
+            $body
         );
+
+        // Get just the scheme and host from the URL.
+        $url_scheme_host_only = parse_url($url, PHP_URL_SCHEME) . '://' . parse_url($url, PHP_URL_HOST);
+
+        // Load the HTML into a DOMDocument.
+        libxml_use_internal_errors(true);
+        $html = new \DOMDocument();
+        $html->loadHTML($body);
+
+        // Convert any relative URLs to absolute URLs in the HTML DOM.
+        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('a'), 'href', $url_scheme_host_only);
+        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('link'), 'href', $url_scheme_host_only);
+        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('img'), 'src', $url_scheme_host_only);
+        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('script'), 'src', $url_scheme_host_only);
+        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('form'), 'action', $url_scheme_host_only);
+
+        // Save HTML.
+        $resource = $html->saveHTML();
+
+        // If the result is false, return a blank string.
+        if (!$resource) {
+            throw new \Exception(sprintf('Could not parse %s', $url));
+        }
+
+        // Remove some HTML tags that DOMDocument adds, returning the output.
+        // We do this instead of using LIBXML_HTML_NOIMPLIED in loadHTML(), because Legacy Forms
+        // are not always contained in a single root / outer element, which is required for
+        // LIBXML_HTML_NOIMPLIED to correctly work.
+        $resource = $this->strip_html_head_body_tags($resource);
+
+        return $resource;
     }
 
     /**
-     * Adds a subscriber to a form by email address
+     * Performs an API request using Guzzle.
      *
-     * @param integer $form_id       Form ID.
-     * @param string  $email_address Email Address.
+     * @param string                                                                                                     $endpoint API Endpoint.
+     * @param string                                                                                                     $method   Request method.
+     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
      *
-     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form-by-email-address
+     * @throws \Exception If JSON encoding arguments failed.
      *
      * @return false|mixed
      */
-    public function add_subscriber_to_form_by_email(int $form_id, string $email_address)
+    public function request(string $endpoint, string $method, array $args = [])
     {
-        return $this->post(
-            endpoint: sprintf('forms/%s/subscribers', $form_id),
-            args: ['email_address' => $email_address]
+        // Build URL.
+        $url = $this->api_url_base . $this->api_version . '/' . $endpoint;
+
+        // Log request.
+        $this->create_log(sprintf('%s %s', $method, $endpoint));
+        $this->create_log(sprintf('%s', json_encode($args)));
+
+        // Build request.
+        switch ($method) {
+            case 'GET':
+                if ($args) {
+                    $url .= '?' . http_build_query($args);
+                }
+
+                $request = new Request(
+                    method: $method,
+                    uri: $url,
+                    headers: $this->get_request_headers(),
+                );
+                break;
+
+            default:
+                $request = new Request(
+                    method:  $method,
+                    uri:     $url,
+                    headers: $this->get_request_headers(),
+                    body:    (string) json_encode($args),
+                );
+                break;
+        }//end switch
+
+        // Send request.
+        $this->response = $this->client->send(
+            $request,
+            ['exceptions' => false]
         );
+
+        // Get response.
+        $response_body = $this->response->getBody()->getContents();
+
+        // Log response.
+        $this->create_log(sprintf('Response Status Code: %s', $this->response->getStatusCode()));
+        $this->create_log(sprintf('Response Body: %s', $response_body));
+        $this->create_log('Finish request successfully');
+
+        // Return response.
+        return json_decode($response_body);
     }
 
     /**
-     * Adds a subscriber to a form by subscriber ID
-     *
-     * @param integer $form_id       Form ID.
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form
+     * Returns the response interface used for the last API request.
      *
      * @since 2.0.0
      *
-     * @return false|mixed
+     * @return \Psr\Http\Message\ResponseInterface
      */
-    public function add_subscriber_to_form(int $form_id, int $subscriber_id)
+    public function getResponseInterface()
     {
-        return $this->post(sprintf('forms/%s/subscribers/%s', $form_id, $subscriber_id));
+        return $this->response;
     }
 
     /**
-     * List subscribers for a form
+     * Returns the headers to use in an API request.
      *
-     * @param integer   $form_id             Form ID.
-     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
-     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
-     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
-     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
-     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
-     * @param boolean   $include_total_count To include the total count of records in the response, use true.
-     * @param string    $after_cursor        Return results after the given pagination cursor.
-     * @param string    $before_cursor       Return results before the given pagination cursor.
-     * @param integer   $per_page            Number of results to return.
+     * @param string  $type Accept and Content-Type Headers.
+     * @param boolean $auth Include authorization header.
      *
-     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-form
+     * @since 2.0.0
      *
-     * @return false|mixed
+     * @return array<string,string>
      */
-    public function get_form_subscriptions(
-        int $form_id,
-        string $subscriber_state = 'active',
-        \DateTime $created_after = null,
-        \DateTime $created_before = null,
-        \DateTime $added_after = null,
-        \DateTime $added_before = null,
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Build parameters.
-        $options = [];
+    public function get_request_headers(string $type = 'application/json', bool $auth = true)
+    {
+        $headers = [
+            'Accept'       => $type,
+            'Content-Type' => $type . '; charset=utf-8',
+            'User-Agent'   => $this->get_user_agent(),
+        ];
 
-        if (!empty($subscriber_state)) {
-            $options['status'] = $subscriber_state;
-        }
-        if (!is_null($created_after)) {
-            $options['created_after'] = $created_after->format('Y-m-d');
-        }
-        if (!is_null($created_before)) {
-            $options['created_before'] = $created_before->format('Y-m-d');
-        }
-        if (!is_null($added_after)) {
-            $options['added_after'] = $added_after->format('Y-m-d');
-        }
-        if (!is_null($added_before)) {
-            $options['added_before'] = $added_before->format('Y-m-d');
+        // If no authorization header required, return now.
+        if (!$auth) {
+            return $headers;
         }
 
-        // Send request.
-        return $this->get(
-            endpoint: sprintf('forms/%s/subscribers', $form_id),
-            args: $this->build_total_count_and_pagination_params(
-                params: $options,
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Gets sequences
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-sequences
-     *
-     * @return false|mixed
-     */
-    public function get_sequences(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        return $this->get(
-            endpoint: 'sequences',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
+        // Add authorization header and return.
+        $headers['Authorization'] = 'Bearer ' . $this->access_token;
+        return $headers;
     }
 
     /**
-     * Adds a subscriber to a sequence by email address
-     *
-     * @param integer $sequence_id   Sequence ID.
-     * @param string  $email_address Email Address.
+     * Returns the maximum amount of time to wait for
+     * a response to the request before exiting.
      *
-     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence-by-email-address
+     * @since 2.0.0
      *
-     * @return false|mixed
+     * @return integer     Timeout, in seconds.
      */
-    public function add_subscriber_to_sequence_by_email(int $sequence_id, string $email_address)
+    public function get_timeout()
     {
-        return $this->post(
-            endpoint: sprintf('sequences/%s/subscribers', $sequence_id),
-            args: ['email_address' => $email_address]
-        );
-    }
+        $timeout = 10;
 
-    /**
-     * Adds a subscriber to a sequence by subscriber ID
-     *
-     * @param integer $sequence_id   Sequence ID.
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence
-     *
-     * @since 2.0.0
-     *
-     * @return false|mixed
-     */
-    public function add_subscriber_to_sequence(int $sequence_id, int $subscriber_id)
-    {
-        return $this->post(sprintf('sequences/%s/subscribers/%s', $sequence_id, $subscriber_id));
-    }
-
-    /**
-     * List subscribers for a sequence
-     *
-     * @param integer   $sequence_id         Sequence ID.
-     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
-     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
-     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
-     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
-     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
-     * @param boolean   $include_total_count To include the total count of records in the response, use true.
-     * @param string    $after_cursor        Return results after the given pagination cursor.
-     * @param string    $before_cursor       Return results before the given pagination cursor.
-     * @param integer   $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-sequence
-     *
-     * @return false|mixed
-     */
-    public function get_sequence_subscriptions(
-        int $sequence_id,
-        string $subscriber_state = 'active',
-        \DateTime $created_after = null,
-        \DateTime $created_before = null,
-        \DateTime $added_after = null,
-        \DateTime $added_before = null,
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Build parameters.
-        $options = [];
-
-        if (!empty($subscriber_state)) {
-            $options['status'] = $subscriber_state;
-        }
-        if (!is_null($created_after)) {
-            $options['created_after'] = $created_after->format('Y-m-d');
-        }
-        if (!is_null($created_before)) {
-            $options['created_before'] = $created_before->format('Y-m-d');
-        }
-        if (!is_null($added_after)) {
-            $options['added_after'] = $added_after->format('Y-m-d');
-        }
-        if (!is_null($added_before)) {
-            $options['added_before'] = $added_before->format('Y-m-d');
-        }
-
-        // Send request.
-        return $this->get(
-            endpoint: sprintf('sequences/%s/subscribers', $sequence_id),
-            args: $this->build_total_count_and_pagination_params(
-                params: $options,
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * List tags.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-tags
-     *
-     * @return false|array<int,\stdClass>
-     */
-    public function get_tags(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        return $this->get(
-            endpoint: 'tags',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Creates a tag.
-     *
-     * @param string $tag Tag Name.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-tag
-     *
-     * @return false|mixed
-     */
-    public function create_tag(string $tag)
-    {
-        return $this->post(
-            endpoint: 'tags',
-            args: ['name' => $tag]
-        );
-    }
-
-    /**
-     * Creates multiple tags.
-     *
-     * @param array<int,string> $tags         Tag Names.
-     * @param string            $callback_url URL to notify for large batch size when async processing complete.
-     *
-     * @since 1.1.0
-     *
-     * @see https://developers.convertkit.com/v4.html#bulk-create-tags
-     *
-     * @return false|mixed
-     */
-    public function create_tags(array $tags, string $callback_url = '')
-    {
-        // Build parameters.
-        $options = [
-            'tags' => [],
-        ];
-        foreach ($tags as $i => $tag) {
-            $options['tags'][] = [
-                'name' => (string) $tag,
-            ];
-        }
-
-        if (!empty($callback_url)) {
-            $options['callback_url'] = $callback_url;
-        }
-
-        // Send request.
-        return $this->post(
-            endpoint: 'bulk/tags',
-            args: $options
-        );
-    }
-
-    /**
-     * Tags a subscriber with the given existing Tag.
-     *
-     * @param integer $tag_id        Tag ID.
-     * @param string  $email_address Email Address.
-     *
-     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber-by-email-address
-     *
-     * @return false|mixed
-     */
-    public function tag_subscriber_by_email(int $tag_id, string $email_address)
-    {
-        return $this->post(
-            endpoint: sprintf('tags/%s/subscribers', $tag_id),
-            args: ['email_address' => $email_address]
-        );
-    }
-
-    /**
-     * Tags a subscriber by subscriber ID with the given existing Tag.
-     *
-     * @param integer $tag_id        Tag ID.
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber
-     *
-     * @return false|mixed
-     */
-    public function tag_subscriber(int $tag_id, int $subscriber_id)
-    {
-        return $this->post(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
-    }
-
-    /**
-     * Removes a tag from a subscriber.
-     *
-     * @param integer $tag_id        Tag ID.
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber
-     *
-     * @return false|mixed
-     */
-    public function remove_tag_from_subscriber(int $tag_id, int $subscriber_id)
-    {
-        return $this->delete(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
-    }
-
-    /**
-     * Removes a tag from a subscriber by email address.
-     *
-     * @param integer $tag_id        Tag ID.
-     * @param string  $email_address Subscriber email address.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber-by-email-address
-     *
-     * @return false|mixed
-     */
-    public function remove_tag_from_subscriber_by_email(int $tag_id, string $email_address)
-    {
-        return $this->delete(
-            sprintf('tags/%s/subscribers', $tag_id),
-            ['email_address' => $email_address]
-        );
-    }
-
-    /**
-     * List subscribers for a tag
-     *
-     * @param integer   $tag_id              Tag ID.
-     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
-     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
-     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
-     * @param \DateTime $tagged_after        Filter subscribers who have been tagged after this date.
-     * @param \DateTime $tagged_before       Filter subscribers who have been tagged before this date.
-     * @param boolean   $include_total_count To include the total count of records in the response, use true.
-     * @param string    $after_cursor        Return results after the given pagination cursor.
-     * @param string    $before_cursor       Return results before the given pagination cursor.
-     * @param integer   $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-tag
-     *
-     * @return false|mixed
-     */
-    public function get_tag_subscriptions(
-        int $tag_id,
-        string $subscriber_state = 'active',
-        \DateTime $created_after = null,
-        \DateTime $created_before = null,
-        \DateTime $tagged_after = null,
-        \DateTime $tagged_before = null,
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Build parameters.
-        $options = [];
-
-        if (!empty($subscriber_state)) {
-            $options['status'] = $subscriber_state;
-        }
-        if (!is_null($created_after)) {
-            $options['created_after'] = $created_after->format('Y-m-d');
-        }
-        if (!is_null($created_before)) {
-            $options['created_before'] = $created_before->format('Y-m-d');
-        }
-        if (!is_null($tagged_after)) {
-            $options['tagged_after'] = $tagged_after->format('Y-m-d');
-        }
-        if (!is_null($tagged_before)) {
-            $options['tagged_before'] = $tagged_before->format('Y-m-d');
-        }
-
-        // Send request.
-        return $this->get(
-            endpoint: sprintf('tags/%s/subscribers', $tag_id),
-            args: $this->build_total_count_and_pagination_params(
-                params: $options,
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * List email templates.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#convertkit-api-email-templates
-     *
-     * @return false|mixed
-     */
-    public function get_email_templates(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'email_templates',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * List subscribers.
-     *
-     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
-     * @param string    $email_address       Search susbcribers by email address. This is an exact match search.
-     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
-     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
-     * @param \DateTime $updated_after       Filter subscribers who have been updated after this date.
-     * @param \DateTime $updated_before      Filter subscribers who have been updated before this date.
-     * @param string    $sort_field          Sort Field (id|updated_at|cancelled_at).
-     * @param string    $sort_order          Sort Order (asc|desc).
-     * @param boolean   $include_total_count To include the total count of records in the response, use true.
-     * @param string    $after_cursor        Return results after the given pagination cursor.
-     * @param string    $before_cursor       Return results before the given pagination cursor.
-     * @param integer   $per_page            Number of results to return.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#list-subscribers
-     *
-     * @return false|mixed
-     */
-    public function get_subscribers(
-        string $subscriber_state = 'active',
-        string $email_address = '',
-        \DateTime $created_after = null,
-        \DateTime $created_before = null,
-        \DateTime $updated_after = null,
-        \DateTime $updated_before = null,
-        string $sort_field = 'id',
-        string $sort_order = 'desc',
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Build parameters.
-        $options = [];
-
-        if (!empty($subscriber_state)) {
-            $options['status'] = $subscriber_state;
-        }
-        if (!empty($email_address)) {
-            $options['email_address'] = $email_address;
-        }
-        if (!is_null($created_after)) {
-            $options['created_after'] = $created_after->format('Y-m-d');
-        }
-        if (!is_null($created_before)) {
-            $options['created_before'] = $created_before->format('Y-m-d');
-        }
-        if (!is_null($updated_after)) {
-            $options['updated_after'] = $updated_after->format('Y-m-d');
-        }
-        if (!is_null($updated_before)) {
-            $options['updated_before'] = $updated_before->format('Y-m-d');
-        }
-        if (!empty($sort_field)) {
-            $options['sort_field'] = $sort_field;
-        }
-        if (!empty($sort_order)) {
-            $options['sort_order'] = $sort_order;
-        }
-
-        // Send request.
-        return $this->get(
-            endpoint: 'subscribers',
-            args: $this->build_total_count_and_pagination_params(
-                params: $options,
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Create a subscriber.
-     *
-     * Behaves as an upsert. If a subscriber with the provided email address does not exist,
-     * it creates one with the specified first name and state. If a subscriber with the provided
-     * email address already exists, it updates the first name.
-     *
-     * @param string                $email_address    Email Address.
-     * @param string                $first_name       First Name.
-     * @param string                $subscriber_state Subscriber State (active|bounced|cancelled|complained|inactive).
-     * @param array<string, string> $fields           Custom Fields.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-subscriber
-     *
-     * @return mixed
-     */
-    public function create_subscriber(
-        string $email_address,
-        string $first_name = '',
-        string $subscriber_state = '',
-        array $fields = []
-    ) {
-        // Build parameters.
-        $options = ['email_address' => $email_address];
-
-        if (!empty($first_name)) {
-            $options['first_name'] = $first_name;
-        }
-        if (!empty($subscriber_state)) {
-            $options['state'] = $subscriber_state;
-        }
-        if (count($fields)) {
-            $options['fields'] = $fields;
-        }
-
-        // Send request.
-        return $this->post(
-            endpoint: 'subscribers',
-            args: $options
-        );
-    }
-
-    /**
-     * Create multiple subscribers.
-     *
-     * @param array<int,array<string,string>> $subscribers  Subscribers.
-     * @param string                          $callback_url URL to notify for large batch size when async processing complete.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#bulk-create-subscribers
-     *
-     * @return mixed
-     */
-    public function create_subscribers(array $subscribers, string $callback_url = '')
-    {
-        // Build parameters.
-        $options = ['subscribers' => $subscribers];
-
-        if (!empty($callback_url)) {
-            $options['callback_url'] = $callback_url;
-        }
-
-        // Send request.
-        return $this->post(
-            endpoint: 'bulk/subscribers',
-            args: $options
-        );
-    }
-
-    /**
-     * Get the ConvertKit subscriber ID associated with email address if it exists.
-     * Return false if subscriber not found.
-     *
-     * @param string $email_address Email Address.
-     *
-     * @throws \InvalidArgumentException If the email address is not a valid email format.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
-     *
-     * @return false|integer
-     */
-    public function get_subscriber_id(string $email_address)
-    {
-        $subscribers = $this->get(
-            'subscribers',
-            ['email_address' => $email_address]
-        );
-
-        if (!count($subscribers->subscribers)) {
-            $this->create_log('No subscribers');
-            return false;
-        }
-
-        // Return the subscriber's ID.
-        return $subscribers->subscribers[0]->id;
-    }
-
-    /**
-     * Get subscriber by id
-     *
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
-     *
-     * @return false|integer
-     */
-    public function get_subscriber(int $subscriber_id)
-    {
-        return $this->get(sprintf('subscribers/%s', $subscriber_id));
-    }
-
-    /**
-     * Updates the information for a single subscriber.
-     *
-     * @param integer               $subscriber_id Existing Subscriber ID.
-     * @param string                $first_name    New First Name.
-     * @param string                $email_address New Email Address.
-     * @param array<string, string> $fields        Updated Custom Fields.
-     *
-     * @see https://developers.convertkit.com/v4.html#update-a-subscriber
-     *
-     * @return false|mixed
-     */
-    public function update_subscriber(
-        int $subscriber_id,
-        string $first_name = '',
-        string $email_address = '',
-        array $fields = []
-    ) {
-        // Build parameters.
-        $options = [];
-
-        if (!empty($first_name)) {
-            $options['first_name'] = $first_name;
-        }
-        if (!empty($email_address)) {
-            $options['email_address'] = $email_address;
-        }
-        if (!empty($fields)) {
-            $options['fields'] = $fields;
-        }
-
-        // Send request.
-        return $this->put(
-            sprintf('subscribers/%s', $subscriber_id),
-            $options
-        );
-    }
-
-    /**
-     * Unsubscribe an email address.
-     *
-     * @param string $email_address Email Address.
-     *
-     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
-     *
-     * @return false|object
-     */
-    public function unsubscribe_by_email(string $email_address)
-    {
-        return $this->post(
-            sprintf(
-                'subscribers/%s/unsubscribe',
-                $this->get_subscriber_id($email_address)
-            )
-        );
-    }
-
-    /**
-     * Unsubscribe the given subscriber ID.
-     *
-     * @param integer $subscriber_id Subscriber ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
-     *
-     * @return false|object
-     */
-    public function unsubscribe(int $subscriber_id)
-    {
-        return $this->post(sprintf('subscribers/%s/unsubscribe', $subscriber_id));
-    }
-
-    /**
-     * Get a list of the tags for a subscriber.
-     *
-     * @param integer $subscriber_id       Subscriber ID.
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-tags-for-a-subscriber
-     *
-     * @return false|array<int,\stdClass>
-     */
-    public function get_subscriber_tags(
-        int $subscriber_id,
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        return $this->get(
-            endpoint: sprintf('subscribers/%s/tags', $subscriber_id),
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * List broadcasts.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @see https://developers.convertkit.com/v4.html#list-broadcasts
-     *
-     * @return false|mixed
-     */
-    public function get_broadcasts(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'broadcasts',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Creates a broadcast.
-     *
-     * @param string               $subject           The broadcast email's subject.
-     * @param string               $content           The broadcast's email HTML content.
-     * @param string               $description       An internal description of this broadcast.
-     * @param boolean              $public            Specifies whether or not this is a public post.
-     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
-     *                                                only to public posts).
-     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
-     *                                                a draft broadcast. If set to a future time, this is the time that
-     *                                                the broadcast will be scheduled to send.
-     * @param string               $email_address     Sending email address; leave blank to use your account's
-     *                                                default sending email address.
-     * @param string               $email_template_id ID of the email template to use; leave blank to use your
-     *                                                account's default email template.
-     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
-     *                                                (applicable only to public posts).
-     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
-     *                                                post (applicable only to public posts).
-     * @param string               $preview_text      Specify the preview text of the email.
-     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-broadcast
-     *
-     * @return false|object
-     */
-    public function create_broadcast(
-        string $subject = '',
-        string $content = '',
-        string $description = '',
-        bool $public = false,
-        \DateTime $published_at = null,
-        \DateTime $send_at = null,
-        string $email_address = '',
-        string $email_template_id = '',
-        string $thumbnail_alt = '',
-        string $thumbnail_url = '',
-        string $preview_text = '',
-        array $subscriber_filter = []
-    ) {
-        $options = [
-            'email_template_id' => $email_template_id,
-            'email_address'     => $email_address,
-            'content'           => $content,
-            'description'       => $description,
-            'public'            => $public,
-            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
-            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
-            'thumbnail_alt'     => $thumbnail_alt,
-            'thumbnail_url'     => $thumbnail_url,
-            'preview_text'      => $preview_text,
-            'subject'           => $subject,
-        ];
-        if (count($subscriber_filter)) {
-            $options['subscriber_filter'] = $subscriber_filter;
-        }
-
-        // Iterate through options, removing blank entries.
-        foreach ($options as $key => $value) {
-            if (is_string($value) && strlen($value) === 0) {
-                unset($options[$key]);
-            }
-        }
-
-        // If the post isn't public, remove some options that don't apply.
-        if (!$public) {
-            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
-        }
-
-        // Send request.
-        return $this->post(
-            endpoint: 'broadcasts',
-            args: $options
-        );
-    }
-
-    /**
-     * Retrieve a specific broadcast.
-     *
-     * @param integer $id Broadcast ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-a-broadcast
-     *
-     * @return false|object
-     */
-    public function get_broadcast(int $id)
-    {
-        return $this->get(sprintf('broadcasts/%s', $id));
-    }
-
-    /**
-     * Get the statistics (recipient count, open rate, click rate, unsubscribe count,
-     * total clicks, status, and send progress) for a specific broadcast.
-     *
-     * @param integer $id Broadcast ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-stats
-     *
-     * @return false|object
-     */
-    public function get_broadcast_stats(int $id)
-    {
-        return $this->get(sprintf('broadcasts/%s/stats', $id));
-    }
-
-    /**
-     * Updates a broadcast.
-     *
-     * @param integer              $id                Broadcast ID.
-     * @param string               $subject           The broadcast email's subject.
-     * @param string               $content           The broadcast's email HTML content.
-     * @param string               $description       An internal description of this broadcast.
-     * @param boolean              $public            Specifies whether or not this is a public post.
-     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
-     *                                                only to public posts).
-     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
-     *                                                a draft broadcast. If set to a future time, this is the time that
-     *                                                the broadcast will be scheduled to send.
-     * @param string               $email_address     Sending email address; leave blank to use your account's
-     *                                                default sending email address.
-     * @param string               $email_template_id ID of the email template to use; leave blank to use your
-     *                                                account's default email template.
-     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
-     *                                                (applicable only to public posts).
-     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
-     *                                                post (applicable only to public posts).
-     * @param string               $preview_text      Specify the preview text of the email.
-     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
-     *
-     * @see https://developers.convertkit.com/#create-a-broadcast
-     *
-     * @return false|object
-     */
-    public function update_broadcast(
-        int $id,
-        string $subject = '',
-        string $content = '',
-        string $description = '',
-        bool $public = false,
-        \DateTime $published_at = null,
-        \DateTime $send_at = null,
-        string $email_address = '',
-        string $email_template_id = '',
-        string $thumbnail_alt = '',
-        string $thumbnail_url = '',
-        string $preview_text = '',
-        array $subscriber_filter = []
-    ) {
-        $options = [
-            'email_template_id' => $email_template_id,
-            'email_address'     => $email_address,
-            'content'           => $content,
-            'description'       => $description,
-            'public'            => $public,
-            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
-            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
-            'thumbnail_alt'     => $thumbnail_alt,
-            'thumbnail_url'     => $thumbnail_url,
-            'preview_text'      => $preview_text,
-            'subject'           => $subject,
-        ];
-        if (count($subscriber_filter)) {
-            $options['subscriber_filter'] = $subscriber_filter;
-        }
-
-        // Iterate through options, removing blank entries.
-        foreach ($options as $key => $value) {
-            if (is_string($value) && strlen($value) === 0) {
-                unset($options[$key]);
-            }
-        }
-
-        // If the post isn't public, remove some options that don't apply.
-        if (!$public) {
-            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
-        }
-
-        // Send request.
-        return $this->put(
-            endpoint: sprintf('broadcasts/%s', $id),
-            args: $options
-        );
-    }
-
-    /**
-     * Deletes an existing broadcast.
-     *
-     * @param integer $id Broadcast ID.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#delete-a-broadcast
-     *
-     * @return false|object
-     */
-    public function delete_broadcast(int $id)
-    {
-        return $this->delete(sprintf('broadcasts/%s', $id));
-    }
-
-    /**
-     * List webhooks.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#list-webhooks
-     *
-     * @return false|mixed
-     */
-    public function get_webhooks(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'webhooks',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Creates a webhook that will be called based on the chosen event types.
-     *
-     * @param string $url       URL to receive event.
-     * @param string $event     Event to subscribe to.
-     * @param string $parameter Optional parameter depending on the event.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-webhook
-     *
-     * @throws \InvalidArgumentException If the event is not supported.
-     *
-     * @return false|object
-     */
-    public function create_webhook(string $url, string $event, string $parameter = '')
-    {
-        // Depending on the event, build the required event array structure.
-        switch ($event) {
-            case 'subscriber.subscriber_activate':
-            case 'subscriber.subscriber_unsubscribe':
-            case 'subscriber.subscriber_bounce':
-            case 'subscriber.subscriber_complain':
-            case 'purchase.purchase_create':
-                $eventData = ['name' => $event];
-                break;
-
-            case 'subscriber.form_subscribe':
-                $eventData = [
-                    'name'    => $event,
-                    'form_id' => $parameter,
-                ];
-                break;
-
-            case 'subscriber.course_subscribe':
-            case 'subscriber.course_complete':
-                $eventData = [
-                    'name'      => $event,
-                    'course_id' => $parameter,
-                ];
-                break;
-
-            case 'subscriber.link_click':
-                $eventData = [
-                    'name'            => $event,
-                    'initiator_value' => $parameter,
-                ];
-                break;
-
-            case 'subscriber.product_purchase':
-                $eventData = [
-                    'name'       => $event,
-                    'product_id' => $parameter,
-                ];
-                break;
-
-            case 'subscriber.tag_add':
-            case 'subscriber.tag_remove':
-                $eventData = [
-                    'name'   => $event,
-                    'tag_id' => $parameter,
-                ];
-                break;
-
-            default:
-                throw new \InvalidArgumentException(sprintf('The event %s is not supported', $event));
-        }//end switch
-
-        // Send request.
-        return $this->post(
-            'webhooks',
-            [
-                'target_url' => $url,
-                'event'      => $eventData,
-            ]
-        );
-    }
-
-    /**
-     * Deletes an existing webhook.
-     *
-     * @param integer $id Webhook ID.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#delete-a-webhook
-     *
-     * @return false|object
-     */
-    public function delete_webhook(int $id)
-    {
-        return $this->delete(sprintf('webhooks/%s', $id));
-    }
-
-    /**
-     * List custom fields.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#list-custom-fields
-     *
-     * @return false|mixed
-     */
-    public function get_custom_fields(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'custom_fields',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Creates a custom field.
-     *
-     * @param string $label Custom Field label.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-custom-field
-     *
-     * @return false|object
-     */
-    public function create_custom_field(string $label)
-    {
-        return $this->post(
-            endpoint: 'custom_fields',
-            args: ['label' => $label]
-        );
-    }
-
-    /**
-     * Creates multiple custom fields.
-     *
-     * @param array<string> $labels       Custom Fields labels.
-     * @param string        $callback_url URL to notify for large batch size when async processing complete.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#bulk-create-custom-fields
-     *
-     * @return false|object
-     */
-    public function create_custom_fields(array $labels, string $callback_url = '')
-    {
-        // Build parameters.
-        $options = [
-            'custom_fields' => [],
-        ];
-        foreach ($labels as $i => $label) {
-            $options['custom_fields'][] = [
-                'label' => (string) $label,
-            ];
-        }
-
-        if (!empty($callback_url)) {
-            $options['callback_url'] = $callback_url;
-        }
-
-        // Send request.
-        return $this->post(
-            endpoint: 'bulk/custom_fields',
-            args: $options
-        );
-    }
-
-    /**
-     * Updates an existing custom field.
-     *
-     * @param integer $id    Custom Field ID.
-     * @param string  $label Updated Custom Field label.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#update-a-custom-field
-     *
-     * @return false|object
-     */
-    public function update_custom_field(int $id, string $label)
-    {
-        return $this->put(
-            endpoint: sprintf('custom_fields/%s', $id),
-            args: ['label' => $label]
-        );
-    }
-
-    /**
-     * Deletes an existing custom field.
-     *
-     * @param integer $id Custom Field ID.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/#destroy-field
-     *
-     * @return false|object
-     */
-    public function delete_custom_field(int $id)
-    {
-        return $this->delete(sprintf('custom_fields/%s', $id));
-    }
-
-    /**
-     * List purchases.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 1.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#list-purchases
-     *
-     * @return false|mixed
-     */
-    public function get_purchases(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'purchases',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Retuns a specific purchase.
-     *
-     * @param integer $purchase_id Purchase ID.
-     *
-     * @see https://developers.convertkit.com/v4.html#get-a-purchase
-     *
-     * @return false|object
-     */
-    public function get_purchase(int $purchase_id)
-    {
-        return $this->get(sprintf('purchases/%s', $purchase_id));
-    }
-
-    /**
-     * Creates a purchase.
-     *
-     * @param string                         $email_address    Email Address.
-     * @param string                         $transaction_id   Transaction ID.
-     * @param array<string,int|float|string> $products         Products.
-     * @param string                         $currency         ISO Currency Code.
-     * @param string                         $first_name       First Name.
-     * @param string                         $status           Order Status.
-     * @param float                          $subtotal         Subtotal.
-     * @param float                          $tax              Tax.
-     * @param float                          $shipping         Shipping.
-     * @param float                          $discount         Discount.
-     * @param float                          $total            Total.
-     * @param \DateTime                      $transaction_time Transaction date and time.
-     *
-     * @see https://developers.convertkit.com/v4.html#create-a-purchase
-     *
-     * @return false|object
-     */
-    public function create_purchase(
-        string $email_address,
-        string $transaction_id,
-        array $products,
-        string $currency = 'USD',
-        string $first_name = null,
-        string $status = null,
-        float $subtotal = 0,
-        float $tax = 0,
-        float $shipping = 0,
-        float $discount = 0,
-        float $total = 0,
-        \DateTime $transaction_time = null
-    ) {
-        // Build parameters.
-        $options = [
-            // Required fields.
-            'email_address'    => $email_address,
-            'transaction_id'   => $transaction_id,
-            'products'         => $products,
-            'currency'         => $currency, // Required, but if not provided, API will default to USD.
-
-            // Optional fields.
-            'first_name'       => $first_name,
-            'status'           => $status,
-            'subtotal'         => $subtotal,
-            'tax'              => $tax,
-            'shipping'         => $shipping,
-            'discount'         => $discount,
-            'total'            => $total,
-            'transaction_time' => (!is_null($transaction_time) ? $transaction_time->format('Y-m-d H:i:s') : ''),
-        ];
-
-        // Iterate through options, removing blank and null entries.
-        foreach ($options as $key => $value) {
-            if (is_null($value)) {
-                unset($options[$key]);
-                continue;
-            }
-
-            if (is_string($value) && strlen($value) === 0) {
-                unset($options[$key]);
-            }
-        }
-
-        return $this->post('purchases', $options);
-    }
-
-    /**
-     * List segments.
-     *
-     * @param boolean $include_total_count To include the total count of records in the response, use true.
-     * @param string  $after_cursor        Return results after the given pagination cursor.
-     * @param string  $before_cursor       Return results before the given pagination cursor.
-     * @param integer $per_page            Number of results to return.
-     *
-     * @since 2.0.0
-     *
-     * @see https://developers.convertkit.com/v4.html#convertkit-api-segments
-     *
-     * @return false|mixed
-     */
-    public function get_segments(
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        // Send request.
-        return $this->get(
-            endpoint: 'segments',
-            args: $this->build_total_count_and_pagination_params(
-                include_total_count: $include_total_count,
-                after_cursor: $after_cursor,
-                before_cursor: $before_cursor,
-                per_page: $per_page
-            )
-        );
-    }
-
-    /**
-     * Get markup from ConvertKit for the provided $url.
-     *
-     * Supports legacy forms and legacy landing pages.
-     *
-     * Forms and Landing Pages should be embedded using the supplied JS embed script in
-     * the API response when using get_forms() or get_landing_pages().
-     *
-     * @param string $url URL of HTML page.
-     *
-     * @throws \InvalidArgumentException If the URL is not a valid URL format.
-     * @throws \Exception If parsing the legacy form or landing page failed.
-     *
-     * @return false|string
-     */
-    public function get_resource(string $url)
-    {
-        if (!filter_var($url, FILTER_VALIDATE_URL)) {
-            throw new \InvalidArgumentException();
-        }
-
-        $resource = '';
-
-        $this->create_log(sprintf('Getting resource %s', $url));
-
-        // Fetch the resource.
-        $request  = new Request(
-            method: 'GET',
-            uri: $url,
-            headers: $this->request_headers(
-                type: 'text/html',
-                auth: false
-            ),
-        );
-        $response = $this->client->send($request);
-
-        // Fetch HTML.
-        $body = $response->getBody()->getContents();
-
-        // Forcibly tell DOMDocument that this HTML uses the UTF-8 charset.
-        // <meta charset="utf-8"> isn't enough, as DOMDocument still interprets the HTML as ISO-8859,
-        // which breaks character encoding.
-        // Use of mb_convert_encoding() with HTML-ENTITIES is deprecated in PHP 8.2, so we have to use this method.
-        // If we don't, special characters render incorrectly.
-        $body = str_replace(
-            '<head>',
-            '<head>' . "\n" . '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">',
-            $body
-        );
-
-        // Get just the scheme and host from the URL.
-        $url_scheme_host_only = parse_url($url, PHP_URL_SCHEME) . '://' . parse_url($url, PHP_URL_HOST);
-
-        // Load the HTML into a DOMDocument.
-        libxml_use_internal_errors(true);
-        $html = new \DOMDocument();
-        $html->loadHTML($body);
-
-        // Convert any relative URLs to absolute URLs in the HTML DOM.
-        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('a'), 'href', $url_scheme_host_only);
-        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('link'), 'href', $url_scheme_host_only);
-        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('img'), 'src', $url_scheme_host_only);
-        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('script'), 'src', $url_scheme_host_only);
-        $this->convert_relative_to_absolute_urls($html->getElementsByTagName('form'), 'action', $url_scheme_host_only);
-
-        // Save HTML.
-        $resource = $html->saveHTML();
-
-        // If the result is false, return a blank string.
-        if (!$resource) {
-            throw new \Exception(sprintf('Could not parse %s', $url));
-        }
-
-        // Remove some HTML tags that DOMDocument adds, returning the output.
-        // We do this instead of using LIBXML_HTML_NOIMPLIED in loadHTML(), because Legacy Forms
-        // are not always contained in a single root / outer element, which is required for
-        // LIBXML_HTML_NOIMPLIED to correctly work.
-        $resource = $this->strip_html_head_body_tags($resource);
-
-        return $resource;
-    }
-
-    /**
-     * Converts any relative URls to absolute, fully qualified HTTP(s) URLs for the given
-     * DOM Elements.
-     *
-     * @param \DOMNodeList<\DOMElement> $elements  Elements.
-     * @param string                    $attribute HTML Attribute.
-     * @param string                    $url       Absolute URL to prepend to relative URLs.
-     *
-     * @since 1.0.0
-     *
-     * @return void
-     */
-    private function convert_relative_to_absolute_urls(\DOMNodeList $elements, string $attribute, string $url) // phpcs:ignore Squiz.Commenting.FunctionComment.IncorrectTypeHint, Generic.Files.LineLength.TooLong
-    {
-        // Anchor hrefs.
-        foreach ($elements as $element) {
-            // Skip if the attribute's value is empty.
-            if (empty($element->getAttribute($attribute))) {
-                continue;
-            }
-
-            // Skip if the attribute's value is a fully qualified URL.
-            if (filter_var($element->getAttribute($attribute), FILTER_VALIDATE_URL)) {
-                continue;
-            }
-
-            // Skip if this is a Google Font CSS URL.
-            if (strpos($element->getAttribute($attribute), '//fonts.googleapis.com') !== false) {
-                continue;
-            }
-
-            // If here, the attribute's value is a relative URL, missing the http(s) and domain.
-            // Prepend the URL to the attribute's value.
-            $element->setAttribute($attribute, $url . $element->getAttribute($attribute));
-        }
-    }
-
-    /**
-     * Strips <html>, <head> and <body> opening and closing tags from the given markup,
-     * as well as the Content-Type meta tag we might have added in get_html().
-     *
-     * @param string $markup HTML Markup.
-     *
-     * @since 1.0.0
-     *
-     * @return string              HTML Markup
-     */
-    private function strip_html_head_body_tags(string $markup)
-    {
-        $markup = str_replace('<html>', '', $markup);
-        $markup = str_replace('</html>', '', $markup);
-        $markup = str_replace('<head>', '', $markup);
-        $markup = str_replace('</head>', '', $markup);
-        $markup = str_replace('<body>', '', $markup);
-        $markup = str_replace('</body>', '', $markup);
-        $markup = str_replace('<meta http-equiv="Content-Type" content="text/html; charset=utf-8">', '', $markup);
-
-        return $markup;
-    }
-
-    /**
-     * Adds total count and pagination parameters to the given array of existing API parameters.
-     *
-     * @param array<string, string|integer|bool> $params              API parameters.
-     * @param boolean                            $include_total_count Return total count of records.
-     * @param string                             $after_cursor        Return results after the given pagination cursor.
-     * @param string                             $before_cursor       Return results before the given pagination cursor.
-     * @param integer                            $per_page            Number of results to return.
-     *
-     * @since 2.0.0
-     *
-     * @return array<string, string|integer|bool>
-     */
-    private function build_total_count_and_pagination_params(
-        array $params = [],
-        bool $include_total_count = false,
-        string $after_cursor = '',
-        string $before_cursor = '',
-        int $per_page = 100
-    ) {
-        $params['include_total_count'] = $include_total_count;
-        if (!empty($after_cursor)) {
-            $params['after'] = $after_cursor;
-        }
-        if (!empty($before_cursor)) {
-            $params['before'] = $before_cursor;
-        }
-        if (!empty($per_page)) {
-            $params['per_page'] = $per_page;
-        }
-
-        return $params;
-    }
-
-    /**
-     * Performs a GET request to the API.
-     *
-     * @param string                                                             $endpoint API Endpoint.
-     * @param array<string, int|string|boolean|array<string, int|string>|string> $args     Request arguments.
-     *
-     * @return false|mixed
-     */
-    public function get(string $endpoint, array $args = [])
-    {
-        return $this->make_request($endpoint, 'GET', $args);
-    }
-
-    /**
-     * Performs a POST request to the API.
-     *
-     * @param string                                                                                                     $endpoint API Endpoint.
-     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
-     *
-     * @return false|mixed
-     */
-    public function post(string $endpoint, array $args = [])
-    {
-        return $this->make_request($endpoint, 'POST', $args);
-    }
-
-    /**
-     * Performs a PUT request to the API.
-     *
-     * @param string                                                              $endpoint API Endpoint.
-     * @param array<string, bool|integer|string|array<string, int|string>|string> $args     Request arguments.
-     *
-     * @return false|mixed
-     */
-    public function put(string $endpoint, array $args = [])
-    {
-        return $this->make_request($endpoint, 'PUT', $args);
-    }
-
-    /**
-     * Performs a DELETE request to the API.
-     *
-     * @param string                                                     $endpoint API Endpoint.
-     * @param array<string, int|string|array<string, int|string>|string> $args     Request arguments.
-     *
-     * @return false|mixed
-     */
-    public function delete(string $endpoint, array $args = [])
-    {
-        return $this->make_request($endpoint, 'DELETE', $args);
-    }
-
-    /**
-     * Performs an API request using Guzzle.
-     *
-     * @param string                                                                                                     $endpoint API Endpoint.
-     * @param string                                                                                                     $method   Request method.
-     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
-     *
-     * @throws \Exception If JSON encoding arguments failed.
-     *
-     * @return false|mixed
-     */
-    public function make_request(string $endpoint, string $method, array $args = [])
-    {
-        // Build URL.
-        $url = $this->api_url_base . $this->api_version . '/' . $endpoint;
-
-        // Log request.
-        $this->create_log(sprintf('%s %s', $method, $endpoint));
-        $this->create_log(sprintf('%s', json_encode($args)));
-
-        // Build request.
-        switch ($method) {
-            case 'GET':
-                if ($args) {
-                    $url .= '?' . http_build_query($args);
-                }
-
-                $request = new Request(
-                    method: $method,
-                    uri: $url,
-                    headers: $this->request_headers(),
-                );
-                break;
-
-            default:
-                $request = new Request(
-                    method:  $method,
-                    uri:     $url,
-                    headers: $this->request_headers(),
-                    body:    (string) json_encode($args),
-                );
-                break;
-        }//end switch
-
-        // Send request.
-        $this->response = $this->client->send(
-            $request,
-            ['exceptions' => false]
-        );
-
-        // Get response.
-        $response_body = $this->response->getBody()->getContents();
-
-        // Log response.
-        $this->create_log(sprintf('Response Status Code: %s', $this->response->getStatusCode()));
-        $this->create_log(sprintf('Response Body: %s', $response_body));
-        $this->create_log('Finish request successfully');
-
-        // Return response.
-        return json_decode($response_body);
-    }
-
-    /**
-     * Returns the response interface used for the last API request.
-     *
-     * @since 2.0.0
-     *
-     * @return \Psr\Http\Message\ResponseInterface
-     */
-    public function getResponseInterface()
-    {
-        return $this->response;
-    }
-
-    /**
-     * Returns the headers to use in an API request.
-     *
-     * @param string  $type Accept and Content-Type Headers.
-     * @param boolean $auth Include authorization header.
-     *
-     * @since 2.0.0
-     *
-     * @return array<string,string>
-     */
-    private function request_headers(string $type = 'application/json', bool $auth = true)
-    {
-        $headers = [
-            'Accept'       => $type,
-            'Content-Type' => $type . '; charset=utf-8',
-            'User-Agent'   => $this->user_agent(),
-        ];
-
-        // If no authorization header required, return now.
-        if (!$auth) {
-            return $headers;
-        }
-
-        // Add authorization header and return.
-        $headers['Authorization'] = 'Bearer ' . $this->access_token;
-        return $headers;
+        return $timeout;
     }
 
     /**
@@ -2178,7 +452,7 @@ private function request_headers(string $type = 'application/json', bool $auth =
      *
      * @return string
      */
-    private function user_agent()
+    public function get_user_agent()
     {
         return 'ConvertKitPHPSDK/' . self::VERSION . ';PHP/' . phpversion();
     }
diff --git a/src/ConvertKit_API_Traits.php b/src/ConvertKit_API_Traits.php
new file mode 100644
index 0000000..b5fc993
--- /dev/null
+++ b/src/ConvertKit_API_Traits.php
@@ -0,0 +1,1810 @@
+<?php
+/**
+ * ConvertKit API Traits
+ *
+ * @author ConvertKit
+ */
+
+namespace ConvertKit_API;
+
+/**
+ * ConvertKit API Traits
+ */
+trait ConvertKit_API_Traits
+{
+    /**
+     * ConvertKit OAuth Application Client ID
+     *
+     * @var string
+     */
+    protected $client_id = '';
+
+    /**
+     * ConvertKit OAuth Application Client Secret
+     *
+     * @var string
+     */
+    protected $client_secret = '';
+
+    /**
+     * Access Token
+     *
+     * @var string
+     */
+    protected $access_token = '';
+
+    /**
+     * OAuth Authorization URL
+     *
+     * @var string
+     */
+    protected $oauth_authorize_url = 'https://app.convertkit.com/oauth/authorize';
+
+    /**
+     * OAuth Token URL
+     *
+     * @var string
+     */
+    protected $oauth_token_url = 'https://api.convertkit.com/oauth/token';
+
+    /**
+     * Version of ConvertKit API
+     *
+     * @var string
+     */
+    protected $api_version = 'v4';
+
+    /**
+     * ConvertKit API URL
+     *
+     * @var string
+     */
+    protected $api_url_base = 'https://api.convertkit.com/';
+
+
+    /**
+     * Gets the current account
+     *
+     * @see https://developers.convertkit.com/v4.html#get-current-account
+     *
+     * @return false|mixed
+     */
+    public function get_account()
+    {
+        return $this->get('account');
+    }
+
+    /**
+     * Gets the account's colors
+     *
+     * @see https://developers.convertkit.com/v4.html#list-colors
+     *
+     * @return false|mixed
+     */
+    public function get_account_colors()
+    {
+        return $this->get('account/colors');
+    }
+
+    /**
+     * Gets the account's colors
+     *
+     * @param array<string, string> $colors Hex colors.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-colors
+     *
+     * @return false|mixed
+     */
+    public function update_account_colors(array $colors)
+    {
+        return $this->put(
+            'account/colors',
+            ['colors' => $colors]
+        );
+    }
+
+    /**
+     * Gets the Creator Profile
+     *
+     * @see https://developers.convertkit.com/v4.html#get-creator-profile
+     *
+     * @return false|mixed
+     */
+    public function get_creator_profile()
+    {
+        return $this->get('account/creator_profile');
+    }
+
+    /**
+     * Gets email stats
+     *
+     * @see https://developers.convertkit.com/v4.html#get-email-stats
+     *
+     * @return false|mixed
+     */
+    public function get_email_stats()
+    {
+        return $this->get('account/email_stats');
+    }
+
+    /**
+     * Gets growth stats
+     *
+     * @param \DateTime $starting Gets stats for time period beginning on this date. Defaults to 90 days ago.
+     * @param \DateTime $ending   Gets stats for time period ending on this date. Defaults to today.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-growth-stats
+     *
+     * @return false|mixed
+     */
+    public function get_growth_stats(\DateTime $starting = null, \DateTime $ending = null)
+    {
+        return $this->get(
+            'account/growth_stats',
+            [
+                'starting' => (!is_null($starting) ? $starting->format('Y-m-d') : ''),
+                'ending'   => (!is_null($ending) ? $ending->format('Y-m-d') : ''),
+            ]
+        );
+    }
+
+    /**
+     * Get forms.
+     *
+     * @param string  $status              Form status (active|archived|trashed|all).
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_forms(
+        string $status = 'active',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'forms',
+            $this->build_total_count_and_pagination_params(
+                [
+                    'type'   => 'embed',
+                    'status' => $status,
+                ],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Get landing pages.
+     *
+     * @param string  $status              Form status (active|archived|trashed|all).
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-forms
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_landing_pages(
+        string $status = 'active',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'forms',
+            $this->build_total_count_and_pagination_params(
+                [
+                    'type'   => 'hosted',
+                    'status' => $status,
+                ],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Adds a subscriber to a form by email address
+     *
+     * @param integer $form_id       Form ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_form_by_email(int $form_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('forms/%s/subscribers', $form_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Adds a subscriber to a form by subscriber ID
+     *
+     * @param integer $form_id       Form ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-form
+     *
+     * @since 2.0.0
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_form(int $form_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('forms/%s/subscribers/%s', $form_id, $subscriber_id));
+    }
+
+    /**
+     * List subscribers for a form
+     *
+     * @param integer   $form_id             Form ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
+     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-form
+     *
+     * @return false|mixed
+     */
+    public function get_form_subscriptions(
+        int $form_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $added_after = null,
+        \DateTime $added_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($added_after)) {
+            $options['added_after'] = $added_after->format('Y-m-d');
+        }
+        if (!is_null($added_before)) {
+            $options['added_before'] = $added_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('forms/%s/subscribers', $form_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Gets sequences
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-sequences
+     *
+     * @return false|mixed
+     */
+    public function get_sequences(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'sequences',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Adds a subscriber to a sequence by email address
+     *
+     * @param integer $sequence_id   Sequence ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_sequence_by_email(int $sequence_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('sequences/%s/subscribers', $sequence_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Adds a subscriber to a sequence by subscriber ID
+     *
+     * @param integer $sequence_id   Sequence ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#add-subscriber-to-sequence
+     *
+     * @since 2.0.0
+     *
+     * @return false|mixed
+     */
+    public function add_subscriber_to_sequence(int $sequence_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('sequences/%s/subscribers/%s', $sequence_id, $subscriber_id));
+    }
+
+    /**
+     * List subscribers for a sequence
+     *
+     * @param integer   $sequence_id         Sequence ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $added_after         Filter subscribers who have been added to the form after this date.
+     * @param \DateTime $added_before        Filter subscribers who have been added to the form before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-sequence
+     *
+     * @return false|mixed
+     */
+    public function get_sequence_subscriptions(
+        int $sequence_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $added_after = null,
+        \DateTime $added_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($added_after)) {
+            $options['added_after'] = $added_after->format('Y-m-d');
+        }
+        if (!is_null($added_before)) {
+            $options['added_before'] = $added_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('sequences/%s/subscribers', $sequence_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List tags.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-tags
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_tags(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            'tags',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a tag.
+     *
+     * @param string $tag Tag Name.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-tag
+     *
+     * @return false|mixed
+     */
+    public function create_tag(string $tag)
+    {
+        return $this->post(
+            'tags',
+            ['name' => $tag]
+        );
+    }
+
+    /**
+     * Creates multiple tags.
+     *
+     * @param array<int,string> $tags         Tag Names.
+     * @param string            $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 1.1.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-tags
+     *
+     * @return false|mixed
+     */
+    public function create_tags(array $tags, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = [
+            'tags' => [],
+        ];
+        foreach ($tags as $i => $tag) {
+            $options['tags'][] = [
+                'name' => (string) $tag,
+            ];
+        }
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/tags',
+            $options
+        );
+    }
+
+    /**
+     * Tags a subscriber with the given existing Tag.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param string  $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function tag_subscriber_by_email(int $tag_id, string $email_address)
+    {
+        return $this->post(
+            sprintf('tags/%s/subscribers', $tag_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * Tags a subscriber by subscriber ID with the given existing Tag.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#tag-a-subscriber
+     *
+     * @return false|mixed
+     */
+    public function tag_subscriber(int $tag_id, int $subscriber_id)
+    {
+        return $this->post(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
+    }
+
+    /**
+     * Removes a tag from a subscriber.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber
+     *
+     * @return false|mixed
+     */
+    public function remove_tag_from_subscriber(int $tag_id, int $subscriber_id)
+    {
+        return $this->delete(sprintf('tags/%s/subscribers/%s', $tag_id, $subscriber_id));
+    }
+
+    /**
+     * Removes a tag from a subscriber by email address.
+     *
+     * @param integer $tag_id        Tag ID.
+     * @param string  $email_address Subscriber email address.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#remove-tag-from-subscriber-by-email-address
+     *
+     * @return false|mixed
+     */
+    public function remove_tag_from_subscriber_by_email(int $tag_id, string $email_address)
+    {
+        return $this->delete(
+            sprintf('tags/%s/subscribers', $tag_id),
+            ['email_address' => $email_address]
+        );
+    }
+
+    /**
+     * List subscribers for a tag
+     *
+     * @param integer   $tag_id              Tag ID.
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $tagged_after        Filter subscribers who have been tagged after this date.
+     * @param \DateTime $tagged_before       Filter subscribers who have been tagged before this date.
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers-for-a-tag
+     *
+     * @return false|mixed
+     */
+    public function get_tag_subscriptions(
+        int $tag_id,
+        string $subscriber_state = 'active',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $tagged_after = null,
+        \DateTime $tagged_before = null,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($tagged_after)) {
+            $options['tagged_after'] = $tagged_after->format('Y-m-d');
+        }
+        if (!is_null($tagged_before)) {
+            $options['tagged_before'] = $tagged_before->format('Y-m-d');
+        }
+
+        // Send request.
+        return $this->get(
+            sprintf('tags/%s/subscribers', $tag_id),
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List email templates.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-email-templates
+     *
+     * @return false|mixed
+     */
+    public function get_email_templates(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'email_templates',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List subscribers.
+     *
+     * @param string    $subscriber_state    Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param string    $email_address       Search susbcribers by email address. This is an exact match search.
+     * @param \DateTime $created_after       Filter subscribers who have been created after this date.
+     * @param \DateTime $created_before      Filter subscribers who have been created before this date.
+     * @param \DateTime $updated_after       Filter subscribers who have been updated after this date.
+     * @param \DateTime $updated_before      Filter subscribers who have been updated before this date.
+     * @param string    $sort_field          Sort Field (id|updated_at|cancelled_at).
+     * @param string    $sort_order          Sort Order (asc|desc).
+     * @param boolean   $include_total_count To include the total count of records in the response, use true.
+     * @param string    $after_cursor        Return results after the given pagination cursor.
+     * @param string    $before_cursor       Return results before the given pagination cursor.
+     * @param integer   $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-subscribers
+     *
+     * @return false|mixed
+     */
+    public function get_subscribers(
+        string $subscriber_state = 'active',
+        string $email_address = '',
+        \DateTime $created_after = null,
+        \DateTime $created_before = null,
+        \DateTime $updated_after = null,
+        \DateTime $updated_before = null,
+        string $sort_field = 'id',
+        string $sort_order = 'desc',
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($subscriber_state)) {
+            $options['status'] = $subscriber_state;
+        }
+        if (!empty($email_address)) {
+            $options['email_address'] = $email_address;
+        }
+        if (!is_null($created_after)) {
+            $options['created_after'] = $created_after->format('Y-m-d');
+        }
+        if (!is_null($created_before)) {
+            $options['created_before'] = $created_before->format('Y-m-d');
+        }
+        if (!is_null($updated_after)) {
+            $options['updated_after'] = $updated_after->format('Y-m-d');
+        }
+        if (!is_null($updated_before)) {
+            $options['updated_before'] = $updated_before->format('Y-m-d');
+        }
+        if (!empty($sort_field)) {
+            $options['sort_field'] = $sort_field;
+        }
+        if (!empty($sort_order)) {
+            $options['sort_order'] = $sort_order;
+        }
+
+        // Send request.
+        return $this->get(
+            'subscribers',
+            $this->build_total_count_and_pagination_params(
+                $options,
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Create a subscriber.
+     *
+     * Behaves as an upsert. If a subscriber with the provided email address does not exist,
+     * it creates one with the specified first name and state. If a subscriber with the provided
+     * email address already exists, it updates the first name.
+     *
+     * @param string                $email_address    Email Address.
+     * @param string                $first_name       First Name.
+     * @param string                $subscriber_state Subscriber State (active|bounced|cancelled|complained|inactive).
+     * @param array<string, string> $fields           Custom Fields.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-subscriber
+     *
+     * @return mixed
+     */
+    public function create_subscriber(
+        string $email_address,
+        string $first_name = '',
+        string $subscriber_state = '',
+        array $fields = []
+    ) {
+        // Build parameters.
+        $options = ['email_address' => $email_address];
+
+        if (!empty($first_name)) {
+            $options['first_name'] = $first_name;
+        }
+        if (!empty($subscriber_state)) {
+            $options['state'] = $subscriber_state;
+        }
+        if (count($fields)) {
+            $options['fields'] = $fields;
+        }
+
+        // Send request.
+        return $this->post(
+            'subscribers',
+            $options
+        );
+    }
+
+    /**
+     * Create multiple subscribers.
+     *
+     * @param array<int,array<string,string>> $subscribers  Subscribers.
+     * @param string                          $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-subscribers
+     *
+     * @return mixed
+     */
+    public function create_subscribers(array $subscribers, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = ['subscribers' => $subscribers];
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/subscribers',
+            $options
+        );
+    }
+
+    /**
+     * Get the ConvertKit subscriber ID associated with email address if it exists.
+     * Return false if subscriber not found.
+     *
+     * @param string $email_address Email Address.
+     *
+     * @throws \InvalidArgumentException If the email address is not a valid email format.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
+     *
+     * @return false|integer
+     */
+    public function get_subscriber_id(string $email_address)
+    {
+        $subscribers = $this->get(
+            'subscribers',
+            ['email_address' => $email_address]
+        );
+
+        if (!count($subscribers->subscribers)) {
+            return false;
+        }
+
+        // Return the subscriber's ID.
+        return $subscribers->subscribers[0]->id;
+    }
+
+    /**
+     * Get subscriber by id
+     *
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-subscriber
+     *
+     * @return false|integer
+     */
+    public function get_subscriber(int $subscriber_id)
+    {
+        return $this->get(sprintf('subscribers/%s', $subscriber_id));
+    }
+
+    /**
+     * Updates the information for a single subscriber.
+     *
+     * @param integer               $subscriber_id Existing Subscriber ID.
+     * @param string                $first_name    New First Name.
+     * @param string                $email_address New Email Address.
+     * @param array<string, string> $fields        Updated Custom Fields.
+     *
+     * @see https://developers.convertkit.com/v4.html#update-a-subscriber
+     *
+     * @return false|mixed
+     */
+    public function update_subscriber(
+        int $subscriber_id,
+        string $first_name = '',
+        string $email_address = '',
+        array $fields = []
+    ) {
+        // Build parameters.
+        $options = [];
+
+        if (!empty($first_name)) {
+            $options['first_name'] = $first_name;
+        }
+        if (!empty($email_address)) {
+            $options['email_address'] = $email_address;
+        }
+        if (!empty($fields)) {
+            $options['fields'] = $fields;
+        }
+
+        // Send request.
+        return $this->put(
+            sprintf('subscribers/%s', $subscriber_id),
+            $options
+        );
+    }
+
+    /**
+     * Unsubscribe an email address.
+     *
+     * @param string $email_address Email Address.
+     *
+     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
+     *
+     * @return false|object
+     */
+    public function unsubscribe_by_email(string $email_address)
+    {
+        return $this->post(
+            sprintf(
+                'subscribers/%s/unsubscribe',
+                $this->get_subscriber_id($email_address)
+            )
+        );
+    }
+
+    /**
+     * Unsubscribe the given subscriber ID.
+     *
+     * @param integer $subscriber_id Subscriber ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#unsubscribe-subscriber
+     *
+     * @return false|object
+     */
+    public function unsubscribe(int $subscriber_id)
+    {
+        return $this->post(sprintf('subscribers/%s/unsubscribe', $subscriber_id));
+    }
+
+    /**
+     * Get a list of the tags for a subscriber.
+     *
+     * @param integer $subscriber_id       Subscriber ID.
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-tags-for-a-subscriber
+     *
+     * @return false|array<int,\stdClass>
+     */
+    public function get_subscriber_tags(
+        int $subscriber_id,
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        return $this->get(
+            sprintf('subscribers/%s/tags', $subscriber_id),
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * List broadcasts.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @see https://developers.convertkit.com/v4.html#list-broadcasts
+     *
+     * @return false|mixed
+     */
+    public function get_broadcasts(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'broadcasts',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a broadcast.
+     *
+     * @param string               $subject           The broadcast email's subject.
+     * @param string               $content           The broadcast's email HTML content.
+     * @param string               $description       An internal description of this broadcast.
+     * @param boolean              $public            Specifies whether or not this is a public post.
+     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
+     *                                                only to public posts).
+     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
+     *                                                a draft broadcast. If set to a future time, this is the time that
+     *                                                the broadcast will be scheduled to send.
+     * @param string               $email_address     Sending email address; leave blank to use your account's
+     *                                                default sending email address.
+     * @param string               $email_template_id ID of the email template to use; leave blank to use your
+     *                                                account's default email template.
+     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
+     *                                                (applicable only to public posts).
+     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
+     *                                                post (applicable only to public posts).
+     * @param string               $preview_text      Specify the preview text of the email.
+     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-broadcast
+     *
+     * @return false|object
+     */
+    public function create_broadcast(
+        string $subject = '',
+        string $content = '',
+        string $description = '',
+        bool $public = false,
+        \DateTime $published_at = null,
+        \DateTime $send_at = null,
+        string $email_address = '',
+        string $email_template_id = '',
+        string $thumbnail_alt = '',
+        string $thumbnail_url = '',
+        string $preview_text = '',
+        array $subscriber_filter = []
+    ) {
+        $options = [
+            'email_template_id' => $email_template_id,
+            'email_address'     => $email_address,
+            'content'           => $content,
+            'description'       => $description,
+            'public'            => $public,
+            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
+            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
+            'thumbnail_alt'     => $thumbnail_alt,
+            'thumbnail_url'     => $thumbnail_url,
+            'preview_text'      => $preview_text,
+            'subject'           => $subject,
+        ];
+        if (count($subscriber_filter)) {
+            $options['subscriber_filter'] = $subscriber_filter;
+        }
+
+        // Iterate through options, removing blank entries.
+        foreach ($options as $key => $value) {
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        // If the post isn't public, remove some options that don't apply.
+        if (!$public) {
+            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
+        }
+
+        // Send request.
+        return $this->post(
+            'broadcasts',
+            $options
+        );
+    }
+
+    /**
+     * Retrieve a specific broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-broadcast
+     *
+     * @return false|object
+     */
+    public function get_broadcast(int $id)
+    {
+        return $this->get(sprintf('broadcasts/%s', $id));
+    }
+
+    /**
+     * Get the statistics (recipient count, open rate, click rate, unsubscribe count,
+     * total clicks, status, and send progress) for a specific broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-stats
+     *
+     * @return false|object
+     */
+    public function get_broadcast_stats(int $id)
+    {
+        return $this->get(sprintf('broadcasts/%s/stats', $id));
+    }
+
+    /**
+     * Updates a broadcast.
+     *
+     * @param integer              $id                Broadcast ID.
+     * @param string               $subject           The broadcast email's subject.
+     * @param string               $content           The broadcast's email HTML content.
+     * @param string               $description       An internal description of this broadcast.
+     * @param boolean              $public            Specifies whether or not this is a public post.
+     * @param \DateTime            $published_at      Specifies the time that this post was published (applicable
+     *                                                only to public posts).
+     * @param \DateTime            $send_at           Time that this broadcast should be sent; leave blank to create
+     *                                                a draft broadcast. If set to a future time, this is the time that
+     *                                                the broadcast will be scheduled to send.
+     * @param string               $email_address     Sending email address; leave blank to use your account's
+     *                                                default sending email address.
+     * @param string               $email_template_id ID of the email template to use; leave blank to use your
+     *                                                account's default email template.
+     * @param string               $thumbnail_alt     Specify the ALT attribute of the public thumbnail image
+     *                                                (applicable only to public posts).
+     * @param string               $thumbnail_url     Specify the URL of the thumbnail image to accompany the broadcast
+     *                                                post (applicable only to public posts).
+     * @param string               $preview_text      Specify the preview text of the email.
+     * @param array<string,string> $subscriber_filter Filter subscriber(s) to send the email to.
+     *
+     * @see https://developers.convertkit.com/#create-a-broadcast
+     *
+     * @return false|object
+     */
+    public function update_broadcast(
+        int $id,
+        string $subject = '',
+        string $content = '',
+        string $description = '',
+        bool $public = false,
+        \DateTime $published_at = null,
+        \DateTime $send_at = null,
+        string $email_address = '',
+        string $email_template_id = '',
+        string $thumbnail_alt = '',
+        string $thumbnail_url = '',
+        string $preview_text = '',
+        array $subscriber_filter = []
+    ) {
+        $options = [
+            'email_template_id' => $email_template_id,
+            'email_address'     => $email_address,
+            'content'           => $content,
+            'description'       => $description,
+            'public'            => $public,
+            'published_at'      => (!is_null($published_at) ? $published_at->format('Y-m-d H:i:s') : ''),
+            'send_at'           => (!is_null($send_at) ? $send_at->format('Y-m-d H:i:s') : ''),
+            'thumbnail_alt'     => $thumbnail_alt,
+            'thumbnail_url'     => $thumbnail_url,
+            'preview_text'      => $preview_text,
+            'subject'           => $subject,
+        ];
+        if (count($subscriber_filter)) {
+            $options['subscriber_filter'] = $subscriber_filter;
+        }
+
+        // Iterate through options, removing blank entries.
+        foreach ($options as $key => $value) {
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        // If the post isn't public, remove some options that don't apply.
+        if (!$public) {
+            unset($options['published_at'], $options['thumbnail_alt'], $options['thumbnail_url']);
+        }
+
+        // Send request.
+        return $this->put(
+            sprintf('broadcasts/%s', $id),
+            $options
+        );
+    }
+
+    /**
+     * Deletes an existing broadcast.
+     *
+     * @param integer $id Broadcast ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#delete-a-broadcast
+     *
+     * @return false|object
+     */
+    public function delete_broadcast(int $id)
+    {
+        return $this->delete(sprintf('broadcasts/%s', $id));
+    }
+
+    /**
+     * List webhooks.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-webhooks
+     *
+     * @return false|mixed
+     */
+    public function get_webhooks(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'webhooks',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a webhook that will be called based on the chosen event types.
+     *
+     * @param string $url       URL to receive event.
+     * @param string $event     Event to subscribe to.
+     * @param string $parameter Optional parameter depending on the event.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-webhook
+     *
+     * @throws \InvalidArgumentException If the event is not supported.
+     *
+     * @return false|object
+     */
+    public function create_webhook(string $url, string $event, string $parameter = '')
+    {
+        // Depending on the event, build the required event array structure.
+        switch ($event) {
+            case 'subscriber.subscriber_activate':
+            case 'subscriber.subscriber_unsubscribe':
+            case 'subscriber.subscriber_bounce':
+            case 'subscriber.subscriber_complain':
+            case 'purchase.purchase_create':
+                $eventData = ['name' => $event];
+                break;
+
+            case 'subscriber.form_subscribe':
+                $eventData = [
+                    'name'    => $event,
+                    'form_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.course_subscribe':
+            case 'subscriber.course_complete':
+                $eventData = [
+                    'name'      => $event,
+                    'course_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.link_click':
+                $eventData = [
+                    'name'            => $event,
+                    'initiator_value' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.product_purchase':
+                $eventData = [
+                    'name'       => $event,
+                    'product_id' => $parameter,
+                ];
+                break;
+
+            case 'subscriber.tag_add':
+            case 'subscriber.tag_remove':
+                $eventData = [
+                    'name'   => $event,
+                    'tag_id' => $parameter,
+                ];
+                break;
+
+            default:
+                throw new \InvalidArgumentException(sprintf('The event %s is not supported', $event));
+        }//end switch
+
+        // Send request.
+        return $this->post(
+            'webhooks',
+            [
+                'target_url' => $url,
+                'event'      => $eventData,
+            ]
+        );
+    }
+
+    /**
+     * Deletes an existing webhook.
+     *
+     * @param integer $id Webhook ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#delete-a-webhook
+     *
+     * @return false|object
+     */
+    public function delete_webhook(int $id)
+    {
+        return $this->delete(sprintf('webhooks/%s', $id));
+    }
+
+    /**
+     * List custom fields.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-custom-fields
+     *
+     * @return false|mixed
+     */
+    public function get_custom_fields(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'custom_fields',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Creates a custom field.
+     *
+     * @param string $label Custom Field label.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-custom-field
+     *
+     * @return false|object
+     */
+    public function create_custom_field(string $label)
+    {
+        return $this->post(
+            'custom_fields',
+            ['label' => $label]
+        );
+    }
+
+    /**
+     * Creates multiple custom fields.
+     *
+     * @param array<string> $labels       Custom Fields labels.
+     * @param string        $callback_url URL to notify for large batch size when async processing complete.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#bulk-create-custom-fields
+     *
+     * @return false|object
+     */
+    public function create_custom_fields(array $labels, string $callback_url = '')
+    {
+        // Build parameters.
+        $options = [
+            'custom_fields' => [],
+        ];
+        foreach ($labels as $i => $label) {
+            $options['custom_fields'][] = [
+                'label' => (string) $label,
+            ];
+        }
+
+        if (!empty($callback_url)) {
+            $options['callback_url'] = $callback_url;
+        }
+
+        // Send request.
+        return $this->post(
+            'bulk/custom_fields',
+            $options
+        );
+    }
+
+    /**
+     * Updates an existing custom field.
+     *
+     * @param integer $id    Custom Field ID.
+     * @param string  $label Updated Custom Field label.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#update-a-custom-field
+     *
+     * @return false|object
+     */
+    public function update_custom_field(int $id, string $label)
+    {
+        return $this->put(
+            sprintf('custom_fields/%s', $id),
+            ['label' => $label]
+        );
+    }
+
+    /**
+     * Deletes an existing custom field.
+     *
+     * @param integer $id Custom Field ID.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/#destroy-field
+     *
+     * @return false|object
+     */
+    public function delete_custom_field(int $id)
+    {
+        return $this->delete(sprintf('custom_fields/%s', $id));
+    }
+
+    /**
+     * List purchases.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 1.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#list-purchases
+     *
+     * @return false|mixed
+     */
+    public function get_purchases(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'purchases',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Retuns a specific purchase.
+     *
+     * @param integer $purchase_id Purchase ID.
+     *
+     * @see https://developers.convertkit.com/v4.html#get-a-purchase
+     *
+     * @return false|object
+     */
+    public function get_purchase(int $purchase_id)
+    {
+        return $this->get(sprintf('purchases/%s', $purchase_id));
+    }
+
+    /**
+     * Creates a purchase.
+     *
+     * @param string                         $email_address    Email Address.
+     * @param string                         $transaction_id   Transaction ID.
+     * @param array<string,int|float|string> $products         Products.
+     * @param string                         $currency         ISO Currency Code.
+     * @param string                         $first_name       First Name.
+     * @param string                         $status           Order Status.
+     * @param float                          $subtotal         Subtotal.
+     * @param float                          $tax              Tax.
+     * @param float                          $shipping         Shipping.
+     * @param float                          $discount         Discount.
+     * @param float                          $total            Total.
+     * @param \DateTime                      $transaction_time Transaction date and time.
+     *
+     * @see https://developers.convertkit.com/v4.html#create-a-purchase
+     *
+     * @return false|object
+     */
+    public function create_purchase(
+        string $email_address,
+        string $transaction_id,
+        array $products,
+        string $currency = 'USD',
+        string $first_name = null,
+        string $status = null,
+        float $subtotal = 0,
+        float $tax = 0,
+        float $shipping = 0,
+        float $discount = 0,
+        float $total = 0,
+        \DateTime $transaction_time = null
+    ) {
+        // Build parameters.
+        $options = [
+            // Required fields.
+            'email_address'    => $email_address,
+            'transaction_id'   => $transaction_id,
+            'products'         => $products,
+            'currency'         => $currency, // Required, but if not provided, API will default to USD.
+
+            // Optional fields.
+            'first_name'       => $first_name,
+            'status'           => $status,
+            'subtotal'         => $subtotal,
+            'tax'              => $tax,
+            'shipping'         => $shipping,
+            'discount'         => $discount,
+            'total'            => $total,
+            'transaction_time' => (!is_null($transaction_time) ? $transaction_time->format('Y-m-d H:i:s') : ''),
+        ];
+
+        // Iterate through options, removing blank and null entries.
+        foreach ($options as $key => $value) {
+            if (is_null($value)) {
+                unset($options[$key]);
+                continue;
+            }
+
+            if (is_string($value) && strlen($value) === 0) {
+                unset($options[$key]);
+            }
+        }
+
+        return $this->post('purchases', $options);
+    }
+
+    /**
+     * List segments.
+     *
+     * @param boolean $include_total_count To include the total count of records in the response, use true.
+     * @param string  $after_cursor        Return results after the given pagination cursor.
+     * @param string  $before_cursor       Return results before the given pagination cursor.
+     * @param integer $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @see https://developers.convertkit.com/v4.html#convertkit-api-segments
+     *
+     * @return false|mixed
+     */
+    public function get_segments(
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        // Send request.
+        return $this->get(
+            'segments',
+            $this->build_total_count_and_pagination_params(
+                [],
+                $include_total_count,
+                $after_cursor,
+                $before_cursor,
+                $per_page
+            )
+        );
+    }
+
+    /**
+     * Converts any relative URls to absolute, fully qualified HTTP(s) URLs for the given
+     * DOM Elements.
+     *
+     * @param \DOMNodeList<\DOMElement> $elements  Elements.
+     * @param string                    $attribute HTML Attribute.
+     * @param string                    $url       Absolute URL to prepend to relative URLs.
+     *
+     * @since 1.0.0
+     *
+     * @return void
+     */
+    public function convert_relative_to_absolute_urls(\DOMNodeList $elements, string $attribute, string $url) // phpcs:ignore Squiz.Commenting.FunctionComment.IncorrectTypeHint, Generic.Files.LineLength.TooLong
+    {
+        // Anchor hrefs.
+        foreach ($elements as $element) {
+            // Skip if the attribute's value is empty.
+            if (empty($element->getAttribute($attribute))) {
+                continue;
+            }
+
+            // Skip if the attribute's value is a fully qualified URL.
+            if (filter_var($element->getAttribute($attribute), FILTER_VALIDATE_URL)) {
+                continue;
+            }
+
+            // Skip if this is a Google Font CSS URL.
+            if (strpos($element->getAttribute($attribute), '//fonts.googleapis.com') !== false) {
+                continue;
+            }
+
+            // If here, the attribute's value is a relative URL, missing the http(s) and domain.
+            // Prepend the URL to the attribute's value.
+            $element->setAttribute($attribute, $url . $element->getAttribute($attribute));
+        }
+    }
+
+    /**
+     * Strips <html>, <head> and <body> opening and closing tags from the given markup,
+     * as well as the Content-Type meta tag we might have added in get_html().
+     *
+     * @param string $markup HTML Markup.
+     *
+     * @since 1.0.0
+     *
+     * @return string              HTML Markup
+     */
+    public function strip_html_head_body_tags(string $markup)
+    {
+        $markup = str_replace('<html>', '', $markup);
+        $markup = str_replace('</html>', '', $markup);
+        $markup = str_replace('<head>', '', $markup);
+        $markup = str_replace('</head>', '', $markup);
+        $markup = str_replace('<body>', '', $markup);
+        $markup = str_replace('</body>', '', $markup);
+        $markup = str_replace('<meta http-equiv="Content-Type" content="text/html; charset=utf-8">', '', $markup);
+
+        return $markup;
+    }
+
+    /**
+     * Adds total count and pagination parameters to the given array of existing API parameters.
+     *
+     * @param array<string, string|integer|bool> $params              API parameters.
+     * @param boolean                            $include_total_count Return total count of records.
+     * @param string                             $after_cursor        Return results after the given pagination cursor.
+     * @param string                             $before_cursor       Return results before the given pagination cursor.
+     * @param integer                            $per_page            Number of results to return.
+     *
+     * @since 2.0.0
+     *
+     * @return array<string, string|integer|bool>
+     */
+    private function build_total_count_and_pagination_params(
+        array $params = [],
+        bool $include_total_count = false,
+        string $after_cursor = '',
+        string $before_cursor = '',
+        int $per_page = 100
+    ) {
+        $params['include_total_count'] = $include_total_count;
+        if (!empty($after_cursor)) {
+            $params['after'] = $after_cursor;
+        }
+        if (!empty($before_cursor)) {
+            $params['before'] = $before_cursor;
+        }
+        if (!empty($per_page)) {
+            $params['per_page'] = $per_page;
+        }
+
+        return $params;
+    }
+
+    /**
+     * Performs a GET request to the API.
+     *
+     * @param string                                                             $endpoint API Endpoint.
+     * @param array<string, int|string|boolean|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function get(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'GET', $args);
+    }
+
+    /**
+     * Performs a POST request to the API.
+     *
+     * @param string                                                                                                     $endpoint API Endpoint.
+     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function post(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'POST', $args);
+    }
+
+    /**
+     * Performs a PUT request to the API.
+     *
+     * @param string                                                              $endpoint API Endpoint.
+     * @param array<string, bool|integer|string|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function put(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'PUT', $args);
+    }
+
+    /**
+     * Performs a DELETE request to the API.
+     *
+     * @param string                                                     $endpoint API Endpoint.
+     * @param array<string, int|string|array<string, int|string>|string> $args     Request arguments.
+     *
+     * @return false|mixed
+     */
+    public function delete(string $endpoint, array $args = [])
+    {
+        return $this->request($endpoint, 'DELETE', $args);
+    }
+
+    /**
+     * Performs an API request.
+     *
+     * @param string                                                                                                     $endpoint API Endpoint.
+     * @param string                                                                                                     $method   Request method.
+     * @param array<string, bool|integer|float|string|null|array<int|string, float|integer|string|array<string|string>>> $args     Request arguments.
+     *
+     * @throws \Exception If JSON encoding arguments failed.
+     *
+     * @return false|mixed
+     */
+    abstract public function request(string $endpoint, string $method, array $args = []);
+
+    /**
+     * Returns the headers to use in an API request.
+     *
+     * @param string  $type Accept and Content-Type Headers.
+     * @param boolean $auth Include authorization header.
+     *
+     * @since 2.0.0
+     *
+     * @return array<string,string>
+     */
+    abstract public function get_request_headers(string $type = 'application/json', bool $auth = true);
+
+    /**
+     * Returns the maximum amount of time to wait for
+     * a response to the request before exiting.
+     *
+     * @since 2.0.0
+     *
+     * @return integer     Timeout, in seconds.
+     */
+    abstract public function get_timeout();
+
+    /**
+     * Returns the user agent string to use in all HTTP requests.
+     *
+     * @since 2.0.0
+     *
+     * @return string
+     */
+    abstract public function get_user_agent();
+}
diff --git a/tests/ConvertKitAPITest.php b/tests/ConvertKitAPITest.php
index 2d95c73..b6839a3 100644
--- a/tests/ConvertKitAPITest.php
+++ b/tests/ConvertKitAPITest.php
@@ -327,7 +327,7 @@ public function testDebugDisabled()
      */
     public function testRequestHeadersMethod()
     {
-        $headers = $this->callPrivateMethod($this->api, 'request_headers', []);
+        $headers = $this->api->get_request_headers();
         $this->assertArrayHasKey('Accept', $headers);
         $this->assertArrayHasKey('Content-Type', $headers);
         $this->assertArrayHasKey('User-Agent', $headers);
@@ -348,9 +348,9 @@ public function testRequestHeadersMethod()
      */
     public function testRequestHeadersMethodWithType()
     {
-        $headers = $this->callPrivateMethod($this->api, 'request_headers', [
-            'type' => 'text/html',
-        ]);
+        $headers = $this->api->get_request_headers(
+            type: 'text/html'
+        );
         $this->assertArrayHasKey('Accept', $headers);
         $this->assertArrayHasKey('Content-Type', $headers);
         $this->assertArrayHasKey('User-Agent', $headers);
@@ -371,9 +371,9 @@ public function testRequestHeadersMethodWithType()
      */
     public function testRequestHeadersMethodWithAuthDisabled()
     {
-        $headers = $this->callPrivateMethod($this->api, 'request_headers', [
-            'auth' => false,
-        ]);
+        $headers = $this->api->get_request_headers(
+            auth: false
+        );
         $this->assertArrayHasKey('Accept', $headers);
         $this->assertArrayHasKey('Content-Type', $headers);
         $this->assertArrayHasKey('User-Agent', $headers);
@@ -393,10 +393,10 @@ public function testRequestHeadersMethodWithAuthDisabled()
      */
     public function testRequestHeadersMethodWithTypeAndAuthDisabled()
     {
-        $headers = $this->callPrivateMethod($this->api, 'request_headers', [
-            'type' => 'text/html',
-            'auth' => false,
-        ]);
+        $headers = $this->api->get_request_headers(
+            type: 'text/html',
+            auth: false
+        );
         $this->assertArrayHasKey('Accept', $headers);
         $this->assertArrayHasKey('Content-Type', $headers);
         $this->assertArrayHasKey('User-Agent', $headers);