If you have a customer who is delinquent with payments, you may wish to prevent them from booking a class without contacting you first so you can resolve the issue.
You have the ability to add their email to the list that will prevent anyone with that email from making a class reservation. This is located in Manage Settings > Online Reservations at the bottom of the page:
Adding an email to this list will show the person this message when they attempt to reserve:
This message is shown on the public or the members side if you have customer logins enabled on your plan. It will also prevent them from purchasing a pre-pay class.
NOTE: The blocked access does not prevent an admin from creating a reservation for the customer. It also doesn't currently prevent clients from creating an account OR from purchasing a pass.