If a customer needs to modify an invoice that has already been marked as paid, they will need to remove the receipt for the invoice. If the customer as a lot of invoices and receipts in their system, it is recommended to run the processed receipts list report to locate the correct receipt number for the invoice.
Go into Invoices- Reports
Click on the [Sales – Processed receipts list] report. Select the correct customer and period.
In the report, locate the invoice code, and then find the receipt number related to the invoice. Make a note of the receipt number.
Then close the reports section and click on the Customers section under Invoice.
Click on [Tools] at the top of the screen and select [Remove Money In Transaction].
Select the transaction and then click on [Remove].
Go back to the original invoice, unfinalise it, and make the changes needed.