Go to Admin > Settings > Messages.
Booking and appointment messages appear in separate categories when they are available for your business.
With Also send by phone on, the Booking confirmation also goes to the customer by phone, WhatsApp first, then SMS.
When staff book a customer into a class with their credit or membership, the Booking confirmation email does not go to an email you typed at the desk until the customer signs in or you confirm it with a code.
The Appointment confirmation is in the Appointments category and has its own Also send by phone switch. When it is on, the confirmation also goes to the customer by phone, WhatsApp first, then SMS. Email stays on.
The 24-hour reminder is one row for classes and appointments. Its Also send by phone switch covers both: when it is on, the customer also gets the reminder by phone the evening before a class or an appointment, WhatsApp first, then SMS. You do not set classes and appointments separately.
An appointment booked for a group is not sent by phone yet. The person who booked still gets the email.