There can sometimes be scenarios where a client had edited a final invoice. This is usually accepted within Commusoft, however, in these cases, the 'Save' button was not clickable. This invoice was sent to their accounting package.
The type of edit, in these cases, is normally the cause of the issue. You may have edited the 'breakdown type' - in this case, it is not possible to complete this action after it has been sent to an accounting package.
In order to rectify this, please credit the invoice, and create a new invoice in the correct breakdown you require. If this still does not work, contact support for further guidance and troubleshooting steps.