Go to a completed invoice on the transactions table

Click on the invoice, which opens up a view of the invoice

From here you click on the 'Issue Credit Note'-button, which will allow you to create a credit note that references a payment made on an invoice.

Select a reason for issuing the credit note, and select the 'Create Credit Note'-button.

This opens a window into a draft credit note.

Click on the 'Edit Credit Note' button to get to item allocation, and then select the invoice items that will be refunded. This will assign the value of the item to be refunded to the credit note.

Then, click on the 'Issue Credit Note'-button, which creates the credit note, and changes its status from draft to issued.

Go back to the client's transaction table, where you will see the credit note, with a positive balance, as indicated by being in blue. Anything with a positive balance on the transactions table can issued a refund against.

Select the 'Add Refund'-button, which opens up the create refund window, from which you can issue the refund.

Alternatively, a payment that has been created on the client transaction table, but is not yet allocated or has had the allocations removed, can be clicked on and a refund option will be prompted.