In Accepted Practice (AP) mode if you wish to make a change to an invoice, you will need to edit the invoice. By editing the invoice you are ultimately created a duplicate invoice on which to make your changes and the original invoice is closed with credits that close out each line item. 

1. For the desired contact, click the Billing tab.
2. In the Billing section, click the  icon for the invoice that you wish to edit.

   

3. Click Edit Invoice.

   

4. Make the desired changes to the invoice. Note that the invoice number is the original invoice number followed by -c.
5. Click Done