The Receipt must be entered with a Copay amount in the Copay field.
The Received Date on the Receipt must be the same as the Date of Service on the Charge.
The first line item must be a billable Charge.
The line items would need to be re-ordered to move the billable Charge line to the top.
The Payment can be posted from the Receipt; or
Make necessary corrections, and then go back to the Post Charge screen.
The pop-up will display.