To credit an Invoice create a negative invoice in the same manner as a sales invoice. Go to the Customers module and to the Invoices menu, select +Add from the toolbar. Enter the same customer information as the original sales invoice. Keep all fields the same with the exception of the date which can be changed to reflect the date of the credit issue.
Enter product items to be credited, using a negative quantity to reverse the lines from the original sales invoice. The Rate remains a positive value and the Extend GST is recorded as a negative value. Use the same Invoice Date as the original.
When a product with a serial number is entered into the product line, the serial number pop-up window displays.
Tick the Credit Note field.
Enter the serial number of the item. This is a free-text field.
Add another if there is more than one item. Select OK to proceed.
The product line is updated and the Quantity field is a negative value, in line with the number of serial numbers entered.
Post the invoice for issue to your customer.