Transaction codes help us know what is the problem and how to fix it, sbaum.

Code 5008 means that the payment was declined. This is because the details (credit card number, account name, expiration date, and etc.) are entered incorrectly. 

You can contact the credit card holder to double-check the information. If the same error occurs, I'd recommend reaching out to their credit card provider about this. Their support team will be able to get rid of the error.

I've also added an article below about the transactions codes. These codes are applicable to most payment processes: Transaction Result Codes.

After that, you can continue processing the invoice payment.

Let me know if you have follow-up questions.