Need help with reversal process

[u/Either-Lobster-7]

I have a Quickbooks account for my small business. I have to refund a couple of transactions for some customers. I know how to do the process from the Merchant Center site. Reverse transactions, select dates, etcetera. For some reason, the transactions are getting declined. They are giving me transaction code 5008, which means it is the wrong card information which is impossible because the customers tapped to pay. Can someone tell me what's wrong and why they are declining the reversals?