Navigate to CATALOG > Orders in the left menu of the back office and click the order for which you wish to credit shipping costs. You will automatically be taken to the Dashboard of the order in question. In the Invoices area the Create credit invoice button is listed to the right of the title. Click it to credit shipping methods. Leave all products set to a value of 0 (zero) and deactivate the Update stock option. If so desired, you can also notify your customers by ticking the Notify customer check box. The Credit shipping costs option may not be deactivated. Click Save at the right at the bottom of the pop-up window to create the shipping costs credit invoice.
Note: To credit shippings costs only, leave all products set to a value of 0 (zero). It is not possible to undo a credit entry.