Thank you for replying. I have actually repaid the amount now by direct debit into the client's bank account but would like to know what to do if it happens in the future.
I entered the credit card details into the visa payment section (of the invoice pay now section) and received an email saying that the invoice was paid (but it was the wrong invoice). In future, if this were to happen, is there a way to credit the payment back directely onto the credit card via MYOB?
The amount is showing through MYOB as being paid for the incorrect invoice. The money will also go through the bank statement as being paid for the incorrect invoice.