Wrong discount calculation when using multiple fixed discount cart rules

[tiagosampaio]

Preconditions (*)

1. I believe that this happens to any Magento version but I'm using 2.3.7 Commerce Edition currently
2. Create two products with the base price of $19.00 each. Both products must be available to be purchased in the front store.
3. Create two cart discount rules
4. The first cart rule will apply a fixed discount amount of $10.00 to the whole cart. Define a specific coupon code to activate this rule in the shopping cart
5. The second cart rule will apply a fixed discount amount of $18.00 to only one of the products in the cart. This cart rule must be applied automatically to the customer's cart
6. Both cart rules must be active

Steps to reproduce (*)

1. Go to the front store and add the two products in the cart, each one with the price of $19.00 (total $38.00)
2. Go to the cart
3. You should be able to see the second rule already applied and a discount of $18.00 must be visible.
4. In the shopping cart, apply the coupon code to activate the fixed $10.00 discount rule in the cart.
5. You'll be able to see the total discount applied is $24.00 while it should be $28.00
6. The cart total is shown as $14.00 but the correct value should be $10.00

Expected result (*)

1. The discount amount should be $28.00 in total.

Actual result (*)

1. Only a $24.00 discount is applied.

---

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[m2-assistant]

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[m2-assistant]

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[engcom-Oscar]

Hi @tiagosampaio ! Thank you for your report.
Unfortunately, we are not able to reproduce the issue. May you please update description and add more detailed steps to it, like exact rules configuration?
After following steps from the ticket, we got next result:

[tiagosampaio]

1 - Create two products with the price of $19 each (SKUs: test-product-one, test-product-two).
2 - Create two Cart Price Rules:

The first rule is applied only to the product test-product-two (filtered in the actions section)
Applies a fixed discount of $18 on the product's price.

Configuration:

{
"salesrule": [
	{
		"rule_id" : 5,
		"name" : "Test Product Two Discount",
		"description" : "",
		"from_date" : "2021-05-07",
		"to_date" : null,
		"uses_per_customer" : 0,
		"is_active" : 1,
		"conditions_serialized" : "{\"type\":\"Magento\\\\SalesRule\\\\Model\\\\Rule\\\\Condition\\\\Combine\",\"attribute\":null,\"operator\":null,\"value\":true,\"is_value_processed\":null,\"aggregator\":\"all\"}",
		"actions_serialized" : "{\"type\":\"Magento\\\\SalesRule\\\\Model\\\\Rule\\\\Condition\\\\Product\\\\Combine\",\"attribute\":null,\"operator\":null,\"value\":\"1\",\"is_value_processed\":null,\"aggregator\":\"all\",\"conditions\":[{\"type\":\"Magento\\\\SalesRule\\\\Model\\\\Rule\\\\Condition\\\\Product\",\"attribute\":\"sku\",\"operator\":\"==\",\"value\":\"test-product-two\",\"is_value_processed\":false,\"attribute_scope\":\"\"}]}",
		"stop_rules_processing" : 0,
		"is_advanced" : 1,
		"product_ids" : null,
		"sort_order" : 0,
		"simple_action" : "by_fixed",
		"discount_amount" : 18.0000,
		"discount_qty" : null,
		"discount_step" : 0,
		"apply_to_shipping" : 0,
		"times_used" : 0,
		"is_rss" : 1,
		"coupon_type" : 1,
		"use_auto_generation" : 0,
		"uses_per_coupon" : 0,
		"simple_free_shipping" : 0,
		"row_id" : 5,
		"created_in" : 1,
		"updated_in" : 2147483647
	}
]}

The second one applies a fixed discount of $10 to the whole cart.

{
"salesrule": [
	{
		"rule_id" : 6,
		"name" : "Ten Dollars to Whole Cart",
		"description" : "",
		"from_date" : "2021-05-07",
		"to_date" : null,
		"uses_per_customer" : 0,
		"is_active" : 1,
		"conditions_serialized" : "{\"type\":\"Magento\\\\SalesRule\\\\Model\\\\Rule\\\\Condition\\\\Combine\",\"attribute\":null,\"operator\":null,\"value\":true,\"is_value_processed\":null,\"aggregator\":\"all\"}",
		"actions_serialized" : "{\"type\":\"Magento\\\\SalesRule\\\\Model\\\\Rule\\\\Condition\\\\Product\\\\Combine\",\"attribute\":null,\"operator\":null,\"value\":\"1\",\"is_value_processed\":null,\"aggregator\":\"all\"}",
		"stop_rules_processing" : 0,
		"is_advanced" : 1,
		"product_ids" : null,
		"sort_order" : 0,
		"simple_action" : "cart_fixed",
		"discount_amount" : 10.0000,
		"discount_qty" : null,
		"discount_step" : 0,
		"apply_to_shipping" : 0,
		"times_used" : 0,
		"is_rss" : 1,
		"coupon_type" : 2,
		"use_auto_generation" : 0,
		"uses_per_coupon" : 0,
		"simple_free_shipping" : 0,
		"row_id" : 6,
		"created_in" : 1,
		"updated_in" : 2147483647
	}
]}

3 - With all set then go to the storefront and add test-product-one and test-product-two to the cart.
4 - Go to the shopping cart page and you'll be able to see the discount of -$18.00 already applied because test-product-two is in the cart.

5 - Apply the coupon code to the cart
6 - Check the discount amount now

The version I used for this testing is Magento Commerce 2.4.2-p1

[tiagosampaio]

@engcom-Oscar any update on this?

[engcom-Oscar]

@tiagosampaio Thank you for your reply, with more detailed steps I was able to reproduce this issue and confirmed it.

[engcom-Foxtrot]

The issue is caused by calculation in \Magento\SalesRule\Helper\CartFixedDiscount::getDiscountAmount, there the whole cart price discount is divided between all cart items. So, for the first cart item, total price is 19 - (10 / 2) = $14, and for the second one 19 - (10 / 2) - 18 = -4, that becames $0. Finally, the cart total is 14 + 0 = $14.

[engcom-Oscar]

After investigating this issue, we found out that problem caused by wrong sequence of applying cart price rules.

Preconditions (*)

1. Magento version 2.4-develop
2. Create two products with the base price of $19.00 each. Both products must be available to be purchased in the front store.
3. Create first cart rule with fixed discount amount of $10.00 to the whole cart. Define a specific coupon code to activate this rule in the shopping cart
4. Create second cart rule with fixed discount amount of $18.00 to only one of the products in the cart. This cart rule must be applied automatically to the customer's cart

Steps to reproduce (*)

1. Go to the front store and add two created products to the cart, each one with the price of $19.00 (total $38.00)
2. Go to the cart page
3. Apply the coupon code to activate the fixed $10.00 discount rule in the cart.

Actual result (*)

Primarily discount calculating by second rule ($10 for whole cart by coupon) and it using formula sum of discount divided on qty of order items: $10 / 2 = $5 on each product. This make price of both product $19 - $5 = $14, and subtotal of the cart = $28. After this first cart rule applying (minus $18 for one of the product), but because our product price only $14, so discount is only $14, and product's price became 0. Therefore only $24 discount is applied, and the cart total is shown as $14.00.

Expected result (*)

Primarily discount calculating should be by first cart rule (minus $18 for one of the product), to make product price $19 - $18 = $1, cart total = $20. Then second rule should be applying correctly ($10 for whole cart by coupon), to make cart total $10.00. Total discount amount should be $28.00

[artskirk]

@magento I am working on this

[engcom-Bravo]

@magento give me 2.4-develop instance

[magento-deployment-service]

Hi @engcom-Bravo. Thank you for your request. I'm working on Magento instance for you.

[magento-deployment-service]

Hi @engcom-Bravo, here is your Magento Instance: https://c0a44b9caa363e941ccaf50aad1a6c7d.instances-prod.magento-community.engineering
Admin access: https://c0a44b9caa363e941ccaf50aad1a6c7d.instances-prod.magento-community.engineering/admin_20d8
Login: 6a8562de
Password: c8629bbcf037

[engcom-Delta]

@magento give me 2.4-develop instance

[magento-deployment-service]

Hi @engcom-Delta. Thank you for your request. I'm working on Magento instance for you.

[magento-deployment-service]

Hi @engcom-Delta, here is your Magento Instance: https://c0a44b9caa363e941ccaf50aad1a6c7d.instances-prod.magento-community.engineering
Admin access: https://c0a44b9caa363e941ccaf50aad1a6c7d.instances-prod.magento-community.engineering/admin_da8d
Login: 19d98d99
Password: 3c1428b69d2e

[engcom-Delta]

Hi @tiagosampaio ,

Thank you for reporting and collaboration.
Verified the issue on Magento 2.4-develop and the issue is not reproducible. Kindly refer the screenshots.

Steps to reproduce -

1. Create two products with $19 as price
2. Create two Cart Price Rules:
   The first rule is applied only to the product product2 (filtered in the actions section)
   Applies a fixed discount of $18 on the product's price.
   
3. The second one applies a fixed discount of $10 to the whole cart.
4. With all set then go to the storefront and add product1 and product2 to the cart.
5. Go to the shopping cart page and you'll be able to see the discount of -$18.00 already applied because product2 is in the cart.
6. Apply the coupon code to the cart
7. Check the discount amount now
8. Discount is displaying expected as $28
   
   Kindly recheck the issue on latest Magento 2.4-develop instance and Please let us know if you are still facing any issue.
   Thanks.

[tiagosampaio]

@engcom-Delta, this still happens in version 2.4.7-p1.

I have the following cart rules created:

Fixed $10.00 to the whole cart

Fixed $18.00 to a particular category

When I go to the cart page and add the products to my cart I have the following result:

The total discount applied to my cart should be $28.00, not $23.19.

The Testing Product #2 should receive a fixed $18.00 discount amount, because it belongs to category #4, and the $10.00 should be applied to the whole cart after adding the MY10 discount coupon, according to my rule.

Thanks.