In general, we have a 48 hour rule. This means that appointments cancelled with less than 48 Hours Prior Notice may be invoiced for. The meeting is chargeable because the coach or therapists diary is booked out in your name, and his/her time was therefore unavailable for other fee-paying work.
The coach/therapist will accept a cancellation notified by you directly by email, text/sms or telephone call. The coach/therapist will accept that there are natural pauses in the work that you do together. If usual meetings are suspended because of your holidays, maternity, family circumstance, work schedules etc., that will be fine. Equally, if the coach/therapist requires a break in the usual meetings for similar reasons, the coach/therapist would not expect you to pay for those sessions that the therapist was unable to host.
In the case of meetings that are, quite simply, unattended (missed) without any contact from you, the coach/therapist will always expect to be paid for their unproductive time.