Cancel, and the deposit stays with the house at any notice; narrow force majeure may turn it into credit, and a session cut short earns no refund.
Plans shift more easily at night than by daylight. A dinner runs on, a friend turns up unannounced, a flight moves, a mood fades. The house understands all of that and still keeps the deposit, because what the deposit paid for has already taken place.
There is no free window, no 24-hour cut-off and no percentage handed back for early warning. A week's notice and a message sent as she leaves are treated alike. The cost dates from acceptance: the office confirmed, her availability was locked, other requests for that slot were turned down, travel and coordination were arranged. Notice given afterwards cannot reach back and unwind any of it.
A government ban on operations, or serious illness that makes the service impossible, may count as force majeure. The office decides case by case, and where it accepts, the deposit becomes credit toward a later booking, never cash. A clash in the diary, a meeting that overran, feeling slightly off, a rescheduled flight or a change of heart do not qualify.
A returning client's same-day hour or two, or a booking accepted with a therapist already on her way, commits the same costs if it is cancelled. The office then asks for a cancellation-collateral payment equal to the deposit that booking would have carried: the same rule, collected afterwards instead of before.
A session you end before its time is not refunded, in whole or in part. A therapist may end a session at once, without refund, where her safety or consent is compromised.
Dutch distance-selling law, the Wet Koop op Afstand, which implements the EU Consumer Rights Directive, ordinarily gives a consumer fourteen days to withdraw from a service bought at a distance. That right does not apply to services performed on a specific date or within a fixed time window, the date-specific-service exemption at Article 6:230p of the Dutch Civil Code. A booking for a named hour on a named night falls inside it, so the right does not arise and the house policy governs. The full position is on the cancellation policy page, and the deposit entry lists which bookings carry one.