Your client’s payment might still be on the process to be deposited, christopher378.
Most deposits will take five business days to be completed. Also, it will take longer if it’s the first transaction. Please refer to this article for additional reference: QuickBooks Payments.
If the payments won’t still be deposit after the turnaround time, you can just delete the invoice recorded. You don’t have to process any refund if the funds didn’t hit your bank account.
You can also check this article for more information about how to process a refund: Void or refund transactions in QuickBooks Payments.
Post a question again if you have other concerns or need further assistance.
Why do you suspect he is not a legitimate client? If you did not receive his money, then you have nothing to send back.