What a cancellation costs depends on the notice given: nothing more than 24 hours ahead, half the deposit inside 24 hours, the whole deposit once the therapist has set out.
A booking can be cancelled at any time with a message in the thread, and cancelling never costs damages. The deposit is part of the fee, so what the house keeps on a cancellation is the part of that fee it has already earned by the moment your message lands. Its size depends on your notice.
Two rules sit on top. If another client takes the hour you gave up, the whole deposit is returned. And if you can show that the house lost less than the part it kept, it keeps the smaller figure. No other charge follows a cancellation.
One move costs nothing: ask more than 24 hours before the booked time, for a date within 14 days, and the deposit follows the booking whole. A second move, or one asked for inside the final 24 hours, is measured on the scale as if it were a cancellation sent at that moment; what the scale leaves unkept moves with it.
If the house cannot deliver a booking, through serious illness, a government order or a therapist who cannot come, the choice is yours: the deposit back in full, or held for a new date for as long as you need. A moved flight or a change of mind on your side is a cancellation and follows the scale.
A booking taken without a deposit costs nothing to cancel before your therapist sets out; after that, only the part of the fee her journey represents is asked for. A session you end before its booked time stays payable for the time reserved, because the hour was held for you and cannot go to anyone else. Your therapist decides what a session includes, and where a limit of hers is pressed with her already in your room she ends the visit; the fee for the reserved time stays due on the same footing, the hour held and the journey made, with nothing added.
Articles 6:230m to 6:230z of the Dutch Civil Code give a consumer fourteen days to withdraw from most contracts made at a distance. Article 6:230p lists contracts outside that right, among them services related to leisure activities where the contract fixes a specific date or period. A booking here names an hour on a day, so the fourteen-day right does not arise. The full position is on the cancellation policy page.