Refunds not working with Authorize.Net C# interface

[mikehasabat]

I learned today that none of our client's refund transactions are working. In the past we used the AIM interface and the Credit transaction. It seems once this interface was deprecated, the Credit transaction was the first method to be turned off. We switched to using the C# interface and use the transactionTypeEnum.refundTransaction. As I understand it, this requires:

1. The Id of a settled transaction.
2. The last 4 digits of the credit card used.
3. XXXX as the expiration date.

This works perfectly well in the sandbox, but it seems the production site always returns the same error: "The referenced transaction does not meet the criteria for issuing a credit."

I have used the C# interface to check the status of a transaction the client wants to refund, and it is settled. What else could cause this issue?

Mike

[mikehasabat]

After double-checking the code, I discovered the credit card number supplied is "XXXX" plus the last 4 digits of the card used. Can this cause the error mentioned above? I've found that typically the C# interface returns a null response if the provded credit card number or cvv are malformed, but this isn't happening here.