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If you create a service appointment in Schedule that conflicts with another appointment and double booking is not allowed:
Schedule board
You will receive a message indicating that double booking is not allowed for the resource. You will not be able to create the appointment for that resource. See Creating Additional Appointments for information on creating an appointment from the schedule board.Appointment wizard
The appointment will be created. The Appointment Wizard does not check the double-book set up status. See Using the Appointment Wizard for information on creating appointments with the wizard.
When you create a service appointment in Schedule and double booking is allowed, the appointment is created.