If you can’t modify the invoice, reverse it and create a credit note. Record a new invoice with the correct details.
You need to make corrections to a previously entered Sales invoice or Vendor Bill
Open the invoice and click the blue payment link to access the transaction window. See Access a payment from an invoice in Accounting.
In the transaction, remove the allocation to the invoice.
Save it as a payment on account.
In the Customer Receipt or Supplier Payment window, clear the checkbox for the relevant invoice.
Click Save to update the transaction.
Click Yes to save the unallocated amount as a payment on account. T
he payment is now unallocated, and you can modify the invoice.
Modify the invoice.
Reallocate the payment on account to the invoice.