What is recorded
Each appointment keeps a dated history: when it was booked and by whom, reschedules, cancellations, status changes, payments and refunds, and the notifications sent about it.
Why it matters
When a customer says they were never reminded, or that they cancelled in time, the activity shows what happened and when — with the year, so older bookings are not ambiguous.
Where to look
Open the appointment from Schedule → Appointments. The same events also appear on the client's timeline under Clients.