Credit notes are the most refined way to track refunds. Let's assume that you need to refund an amount back to your customer for which you've already raised an invoice. In this case, you can follow the steps mentioned below:

• Click the "Credit Notes" sub-link under the "Invoices" tab.
• Click the "New Credit Note" button from the right-side of the screen.
• Select the customer and select the items on the Credit Note same as that of the Invoice to match total.
• Click the "Save" button.
• Click the cog wheel, and then click the refund option.
• On the Refund page, enter the refund date, amount, payment method and refund details.
• When you are done, click the Save button.

Now, the refund amount will be updated in the customer's records. You can also check the customer statement to verify the transactions.