We built our online booking feature with that in mind. We built a first come, first-served type of scheduling. When one recipient selects an available time and date that you have sent to multiple clients and begins the booking process, that option will no longer show for any other clients as it kicks off the 15 minute reservation window for the client to complete booking that spot. Once they have confirmed booking, that time will no longer be an option for other clients to book.

If they do not complete booking or the reservation window times out, then the date and time they had selected will be added back to the calendar for someone else to book.

Additionally, if you have multiple booking calendars with the same time slot or overlapping time availability listed, as soon as a client chooses a time slot from one calendar, it will be removed from other calendars to ensure you do not get double booked.