I know what to do to fix this, Rafi Wasir.
You can record a new payment using the Receive Payment option, and then link the second one to the refund. This will zero out the negative balance that's showing in your customer's profile.
- Click the Plus icon.
- Under Customers, select Receive Payment.
- Enter the customer's name.
- Under the Outstanding Transactions list, check the boxes for the payment and refund.
- Click Save & close.
I'll be here if you have any follow-up questions on this.