Thank you for your question.
We had a quick look into your wallee space and into the refund that has failed, the error message reads, "The transaction authorization has been declined by the authorization system." Can you please get in touch with your processor why this refund failed?
As you can see, you were able to refund other customers using the same type of payment in the past. This is specific to this transaction.
Please let us know if we can support you in any other matter by getting in touch with our support team: firstname.lastname@example.org