To customer texts to send your clients about their booking:
Go to Menu >> Booking System
Select SMS updates
Select the SMS you would like to edit
Click Edit message
Write the text you would like to use
Insert dynamic value to include the text specific to the booking. For example, {{ClientFirstName}} will include the first name of the client the SMS is sending to.
Press Done to save your changes
Note - your messages must be less than 160 characters in order to send.