In the event that we tried to refund in the system but shows error. We can explain to the customer that we tried to issue the refund but the system won't let us do it. We can offer a store credit / coupon code that they can use to the store as an alternative for the refund.
PEG20 for $20 discount
GET40 for $40 discount
If they declined, apologize to the customer that we are not able to do anything other than giving store credits. If they want, they can resolve the matter with their issuing bank.