Processing a refund

[Martijn Heuts]

Hello, I am running GNU cash for my business.I created and posted an invoice, which was paid in full.However a day later the client returns the item.THe client also paid sales tax on this invoice.
What is the proper way to process this refund in GNU?I tried via the REFUND field which doesn't seem to process correctly.Also I need to make sure the sales tax is taken care of.
Please help. Thanks and I appreciate it!