When viewing a client on the Client page, you'll see a new tab called Statement. This shows the list of that client's appointments, the state of payment on each one and a running total at the bottom.
You'll be able to work on the invoicing or payments singly or in bulk. Select the appointment(s) and a menu will appear asking which option you'd like to take: Add medical codes, create an invoice or add a payment that you've received.
Clicking on the drop-down arrow on the right will allow you to drill down to view more detail on a specific appointment. If a payment was added by mistake, you can remove it. And clicking on the three vertical dots will let you edit the medical codes.
A similar statement view is available on the Invoices page. Click on the three vertical dots, select Edit and click on the Statement tab. You'll be able to view which appointments form part of that invoice and make changes.