Void or Refund a Payment in WHMCS
Refunds
This applies to most payments including captured/authorized credit card transactions that have already been settled in the nightly credit card batch processing.
Edit the invoice that was overcharged/overpaid
Add a line item documenting the refund using a negative dollar amount
Select the Refund tab to issue a refund
Void Unsettled Credit Card Transaction
This applies to captured/authorized credit card transactions that have not yet been settled in the nightly credit card batch processing.
Log in to the gateway/processor control panel
Void the transaction
Edit the WHMCS transaction
Delete the payment transaction at the bottom
Mark the invoice unpaid, if desired
Delete the WHMCS transaction, if desired
Remove Credit from account
In WHMCS go to Summary, Manage Credits and delete credit created by the CC transaction.