Why can't I change a sent invoice's amount?
Financial edits are available on drafts; posted invoices have a limited details form.
Only drafts allow changes to customer, dates, lines and amounts. Opening full edit for a paid or otherwise noneditable invoice returns to its details with a message. With Edit invoices permission, Edit Details on a posted invoice changes nonfinancial details such as reference, addresses and wording. A void invoice cannot use that form. Correcting financial amounts requires reviewing the appropriate void or payment correction, rather than editing the posted lines. Follow Edit, void or delete an invoice before changing a record with payments.