You can ban clients from booking appointments by going to their client record, then selecting "Ban". Banning a client disables them from scheduling an appointment online with the banned e-mail address.
When they enter their e-mail address during the scheduling process, they'll see this message:
If you’d like, you can customize that message to communicate the details of why they've been banned, like an outstanding balance.
Clients can also be unbanned by clicking "Unban".
Viewing the client's history or an appointment they've booked will show whether the client has been banned from booking appointments online.