Once an invoice is raised it should not really be cancelled so we need an option for us to add a Credit note to the clients account. Rather like the credit system at the moment but it needs to be raised like an invoice and be downloadable in PDF format and instead of invoice in the title it should have credit note.
Or another option would be when an invoice is cancelled it should be raise a credit note that the customer can download automatically and mark the invoice as paid via credit note.

