Open the specific invoice you want to work on, especially when an event has more than one proposal, contract or invoice.
Steps
Open the event and select its Invoices area.
Select the invoice name to open its editor. If a list appears, choose the document you want rather than assuming the first one is the right invoice.
You can also use the event Quick Access menu and select Invoices.
Check the document name, event and client before making changes.
Business editing versus client viewing
The business invoice editor requires the appropriate invoice permissions. A client using their portal sees the documents and payment actions they have been given access to, not the business editing tools.