I had a team member accidentally cancel an ENTIRE class because she hit the wrong "cancel booking" button. To us, "cancel booking" usually refers to "one individual's booking" or "one group's booking". But what actually happened is that it cancelled the whole class (or "appointment"), which if there was both a confirmation modal AND the language said "cancel appointment", it would have been much clearer that we would have been cancelling that whole thing.

It's not common to refer to a single "booking" as something that contains multiple different people. Usually, a booking pertains to an individual or a small group—not the entire collection of individuals attending an appointment.