There is a code returned by the credit card processor when the transaction is approved, usually 5-6 digits. I'm trying to retrieve this code with REST API in their sandbox.
If you are using PayPal Payflow you can see this on the transaction result page when logged in to your Payflow account. This number is also on a printed receipt when you go to a store, it's a very common number to have after an approved CC payment. I have yet to accept a real payment through REST API, just working with sandbox so far. Looking at the response for the sandbox payment and the sale transaction I cannot see anything that looks like the processor authorization code.
Documentation for this authorization code is difficult to research and I don't want to lead anyone astray; I'm not looking for anything related to the auth code used for access and refresh tokens, same name but completely different.