Members are required to register in advance or RSVP for any classes set with a SIZE LIMIT.
Class Check-Ins are simply recorded attendances by a member when arriving to class. If a class has no size limit, only a Check-In is required.
How to use Size Limit
When you add a class to your schedule via ADD CLASS tab, you are given the option to set a SIZE LIMIT. This, of course, sets the maximum number of attendees allowed to register for the class but it also differentiates whether an RSVP is necessary or not.
Classes with no class limit do NOT require an RSVP and therefore only a check-in is necessary when arriving for class.
Classes with a class limit set will require an RSVP in advance. The member can do this on their phones or from their desktop profile by going to the Schedule. Upon arriving for class they would Check-In and confirm their attendance like normal.
You can set how far in advance your members can RSVP to a class as well as how soon before the class they can cancel their registration under Triib Settings > Online Settings > Schedule/RSVP Set Up.