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, in the Admin's Transactions panel click on the ID link for this transaction and view the full 'session ID' (or export your cash-out-log and identify it there).
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, you may 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.