Refund an Overpayment
When your client overpays an invoice and would like a refund of the overpaid amount (credit on account), please follow these steps:
Go to the Customer Account > Payment Tab
Find the payment with the overpayment: it will have an amount in the Unapplied Amount column
Click the drop down arrow to the right of the Edit Button, select REFUND
In the Refund window, input the total amount to refund and a memo about the refund in the Note text box
Click Save & Apply to complete the refund