If a 1-confirmation cash-out transaction has not yet been redeemed, you may cancel it if needed so it will no longer be redeemble.
To do so, export your cash-out-log and locate the 'session ID' for the transaction in question.
For example, if the session ID is: b4921f99-0589-419c-b8cf-089d08b12900, then in your server run:
You should see the result 'success'. After which, it is safe to refund the coins or disburse the fiat manually to the customer.
Note: The command will output 'success' whether or not a transaction has already been dispensed or cancelled. So please refer to the dispensed column in your transaction logs as the arbiter of the transaction's status.