Navigate to "Settings"
Find the "Takeoff and Estimate" section on the left
Under this section, click "Payments"
Find the area labeled "ArcSite Payments"
Click the button labeled "View All Transactions"
Locate the payment that needs to be refunded from the list, and click on it
You will get a pop-up that shows the details of the transaction, as well as a "Refund" button at the bottom:
Please allow 5-7 days for a refund to fully complete the process.