Make payment for a pending appointment

Hi there,

I have a problem with making payment with A+. The current system saves an appt right after user click "Confirm appointment", even without payment. So the case is, if user hit confirm then navigate somewhere else, how does he make payment for his pending appt later?

I'm thinking of some solutions:
1. Show a button next to each pending appt (front-end).
2. Send request for payment emails after certain periods of time, and display warning text/popup to the user to remind him.

Please help me implement one of the above solutions, or show me the right way to solve my problem. I'm relatively new to Wordpress and Php, so please be as detailed as possible.
Thank you very much.