1. Create a new invoice. If multiple items are being returned, you can duplicate the original invoice and modify the quantity of the items being returned
2. Add the item being returned to the invoice (in not on the invoice yet)
3. Select the line item from the right side of the sales document section
4. In the Qty field enter -1

To enter negative numbers first enter the number [1] and then tap the minus [-] button on the numeric keyboard.

5. Tap Accept
6. The total amount will become negative (refund). Apply a payment to record the refund.