Navigate to the Transactions section of the dashboard & select the option through which your customer has made a payment. (In this case, via an invoice)
Search using the Date range required & click on Search. You shall see a red failed status beside the transaction as visible below, click on the ⋮ button & click on the Reconcile option.
Post this the page will reload with a message saying Transaction has been reconciled.
Search using the Transaction ID & it should get updated as successful. If the transaction is still showing as Failed in case money has been debited the same will reverted back in 7-9 working days.
Click here to learn how to refund a transaction!