Select Add new service using the purple button on the side bar.
Select service type: Lesson
Select any staff members who you may want to perform this service.
Ensure this service is only available to clients if you invite them by:
Switching Bookable by everyone visiting your booking page to No.
Switch Bookable only by clients you select to No.
Select Create service
Now you can use the service you just created to invite your clients to lessons by selecting a timeslot in your calendar by 'press and hold' on a timeslot that you want to invite clients to in your calendar and then select + Lesson.
Select a coach, clients to invite, a location, service type Lesson, then select the service. Double check the day and time is what you want and finally select the payment method.
Your clients will receive a lesson invitation like this: