Is there a specific app this action is for?
Quickbooks

Please provide a link to the relevant API docs for the specific service / operation.

Invoicing

1. Create Invoice
   Docs: Create an Invoice
   Endpoint: POST /v3/company//invoice

2. Send Invoice
   Docs: Send an Invoice
   Endpoint: POST /v3/company//invoice//send

3. Update Invoice
   Docs: Update an Invoice
   Endpoint: POST /v3/company//invoice?operation=update

4. Void Invoice
   Docs: Void an Invoice
   Endpoint: POST /v3/company//invoice?operation=void

Purchase Orders
5. Create Purchase Order
Docs: [Create a Purchase Order](https://developer.intuit.com/app/developer/qbo/docs/api/accounting/all-entities/purchaseorder#create-a-purchaseorder
Endpoint: POST /v3/company//purchaseorder

Quotes (Estimates)
6. Create Estimate
Docs: Create an Estimate
Endpoint: POST /v3/company//estimate

7. Send EstimateDocs: Send an EstimateEndpoint: POST /v3/company//estimate//send8. Update Estimate
   Docs: Update an Estimate
   Endpoint: POST /v3/company//estimate?operation=update

Official API Reference:
QuickBooks Online API Reference