bookto combines your event type's open hours with your connected calendar and existing bookto appointments. Times that overlap a busy calendar block or another confirmed appointment are not offered. Buffers, minimum notice, booking horizon and the event type's daily limit also apply.
bookto checks free/busy information, not the titles or details of your other events. In Google Calendar, an event marked Free does not block a slot; mark time Busy or Out of office if you do not want it booked.
After an appointment is confirmed, bookto adds its own event to the connected calendar when the connection allows it. If calendar sync fails, the appointment remains in bookto and the dashboard can retry the calendar update. The appointment in bookto is the source of truth.
If bookto cannot check the selected calendar, it offers no slots rather than treating the calendar as free. See Troubleshooting booking availability.