When a customer has paid an invoice with a credit card, you can simply click the Refund button on the invoice (under Invoice History).
If the customer used a different payment method, the easiest way is to add a credit to the invoice, so that the invoice amount is not showing as due anymore.
Here’s how to credit a refund on an invoice:
Log in to ZipBooks and select Invoices from the menu.
Find the invoice that contains the amount you refunded to your customer and click on it.
Click the gray Edit button at the top of the invoice.
Scroll down to the Task and Item sections and click on either the ‘+Task’ or ‘+Item’ button.
For the Title, write Refund, and add any details about the refund in the Description section.
In the Rate or Price fields (depending on if you chose to make the line item a Task or an Item), put the amount you refunded, with a minus sign (-) before it, and put a 1 in the Hours, or Qty box. This will create a credit, and will cancel out the amount due. If you only refunded part of the amount of the invoice, the portion that still applies will remain on the invoice.
Click the blue Save button at the top of the invoice.
By doing this and reversing the amount due, any payment reminders you set up for your overdue invoices will no longer apply to this one (unless a portion of the invoice remains to be paid).
Note: The "Refund" button may only be available for Square and Stripe payments.