Turn off SMS notification when an administrator creates a booking

To turn off SMS notifications when creating an appointment in the Appointment Calendar, go to the Settings — System settings — Notifications section and open the Types of notifications tab and switch off the Creating a booking via Appointment Calendar notification. If necessary, you’ll be able to turn this notification on in the same section. 

Despite switching off this type of notification you can still send SMS with details of the booking individually.

To do this, when creating an appointment go to the Notifications tab in the Booking and check the box next to SMS in the Appointment reminder.

Also here you can change the time of sending a reminder to the client about the forthcoming appointment (more details in this article).