Cancellations and no-shows
Cancelling a booking, the customer's own cancel link, and recording someone who never turned up.
A booking can be called off by you or by the customer, and someone who simply never arrives is recorded differently again. All three end up visible in the diary under All.
Cancelling from the diary
Cancel on a booking needs a staff PIN, records who did it, and emails the customer if confirmation emails are switched on. A cancelled booking frees its time slot back up, so somebody else can book it.
The customer's own cancel link
Every confirmation email carries a link that lets the customer cancel without ringing you. Using it cancels the booking exactly as cancelling from the diary does, and the freed slot goes back on offer.
The link stops working once the booking has become a repair ticket. At that point the device is with you and there is nothing left to cancel unilaterally.
No-shows
No-show is for the customer who booked and never turned up. It needs a staff PIN and records who marked it, and it deliberately sends the customer nothing — it is your note about what happened, not a message to them.
A no-show does notfree the slot back up. The time was held, the bench was blocked, and the day's capacity should reflect that rather than pretending the booking never existed.
Nothing is sent between the confirmation and the appointment. If reminders matter to you, the diary is what to work from — filter to the day and call or message the customers on it.