With the add-only, no details permission, a person can only add events and modify them in the same browser session, within the same 30-minute time window.
Other events that have been previously added show as Reserved.
A client can make an appointment by adding an event on the desired date/time and put their information (name, number, etc.) in the event details. Other clients would not be able to see this information. They will only see an event called "Reserved" on the calendar.
You can then review the appointment requests and contact the client to confirm.
To prevent clients from booking appointments on dates/times when you are not available, you can create "Unavailable" events to block those times as explained here.
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