Note: All pages below are subject to having relevant Roles and Permissions.
Go to Accounts Receivable and select Refunds.
Click on the Add button, select the Customer, complete the Refund details and click on the Refund button.
Select the Customer and complete the other details per the above screen.
As the system is currently configured, you cannot make a Refund unless the account is in Credit.
(The idea being that any Credit would be offset against future invoices). This is being reviewed.