Restrict Client from Booking Appointments

You can disable the ability for a client to schedule appointments directly from the client's profile. Navigate to  Client Profile > Actions > Settings. Uncheck the box for 'schedule appointments.'

This will disable scheduling on a per-client basis.

We cover more on this section here: Client Portal Settings

After this is done, if it's a client that you do not plan on seeing in the future, you're welcome to archive their account. Active and Archived Clients