Once you've approved (non-integrated companies) or published (integrated companies) an invoice, the fields won't be editable and will show as greyed-out.
If you need to edit the invoice after validation, you can unapprove or unpublish it.
This can be necessary if you've assigned incorrect nominal categories.
From the invoice details
From the Inbox or Activity tab, click View beside the invoice to access it.
Click the unpublish or unapprove button.
From the Inbox or Archive
You can unapprove or unpublish one or several invoices from the Inbox or Archive tabs.
Access the Inbox or Archive tab.
Tick the boxes to the left to select the relevant invoices.
From the Actions menu, click Unapprove or Unpublish.
Once unapproved or unpublished, the dropdown menus and text fields will be available for you to edit.
📎NOTE: Marking an invoice as unpublished doesn't delete it from your accounting software. If you're republishing the invoice to your accounting software, you must delete the first instance of it manually from the software.