You may need to refund a customer for an overpayment. For that:
- The client must be marked as a ‘Billing Client’.
- The client must have a negative balance, i.e., over payment.
To refund a client in ArchiOffice/EngineerOffice:
1. Begin by applying the overpayment. E.g., we have an open invoice for $10,000; you must apply the first payment of $10,000 to it in the Transaction Detail screen.
This sets the Project Balance to $0.
2. Now enter a second payment, which is basically the overpayment or amount to be refunded (say $500). 
After you apply this payment, it goes to the bottom section marked as Type OP.
3. After confirming it, the payment appears as a negative balance for the project.
4. Next step is to refund the overpayment. Go to the Contacts > Transactions tab.
5. Click the Refund link at the bottom. You are prompted to issue a full refund; click Full to start the refund process.
6. The Transaction Detail screen opens with the refund details. Apply the refund to the correct project in the list. 
7. The payment is marked as Type RF (refund). Click Done to complete the process.
8. To verify, go to the Projects > Billing > Transactions screen.