Recurring reservations don't support Appointments. This is because appointments are not added to the calendar until the customer books them. If you have clients who attend the same day/time on a regular basis, we'd recommend using the Classes feature, which does work with recurring reservations. Classes can be set to have a limit of 1 attendee just like appointments do.
To do this, you'll need to create and schedule a repeating one-on-one class. To do this, see How to run one-on-one sessions with a pre-set timetable.
Once done, you'll be able to set up a recurring reservation for your client.