Appointment Requests Confirming Without Payment Being Complete

Hello,

I have set Appointments + to Auto Confirm and accept payments via PayPal.

When a client selects an appointment and the payment screen appears they can confirm the appointment and not make any payment and the appointment is immediately reserved for them.

Also if a client selects a time slot and then goes to PayPal but cancels the transaction the time slot shows as available but when selected again a message appears to say that the slot is unavailable.

Is there a way to configure the system such that the appointment is only confirmed once the payment has been processed by PayPal successfully?

A link to the page is http://hearthealthscreenings.com/restore/

The short codes used are;
[app_monthly_schedule ... service="2"]
[app_pagination month="1"]
[app_login]
[app_confirmation]
[app_paypal ... item_name=" Deposit for SERVICE"]

Thanks for your help