Click Cash Out on the Invoice.
Choose the payment method. (cash is used in this example)
This is the normal cash out process. You clicked enter to send the payment through and bring you to the print or email receipt screen.
If the customer change their mind when you get to this screen, click Cancel.
When you click cancel a warning pops up. Click Yes to refund the payment.
After clicking Yes, it brings you back to the Cash Out screen. Choose the same payment method previously used. Click Yes to accept the full amount. You will enter in a negative amount.
Enter the negative dollar amount. Click Enter. The Change Returned and Total Paid will change back as if you are first cashing out the invoice.
Now you can choose the desired payment method and proceed with the cash out as normal.