Invoice Statuses:

There are 3 statuses that invoices can be in:

1. Draft – When an invoice is in this status, it can be edited.
2. Approved – In this status the invoice is ready to be sent to a customer and cannot be edited. 
3. Paid – An invoice will only get to this status if you click on Options and select Mark as Paid.

Revert to Draft:

If there is an error on an invoice and it is out of the draft status. You are able to click Options and select Revert to Draft.