How can I record an offline refund?

Let's say you need to refund a client in an 'offline' (Cash, check, etc) format.
To get started, head on over to the Billing section of the project and click 'Issue Refund'

From here, you can select the payment you want to refund and change the origin to "offline"

You'll now be able to see your refund back underneath "Payments"