📄️Cancel a booking
Cancels a booking. Some providers answer `cancellation_pending` first; poll booking-details until `booking.status` is `cancelled`. Only bookings made with your account can be cancelled (`404` otherwise); a modified `supplier_reference` answers `422 invalid_booking_token`. A booking TransferPlatform already cancelled is answered from its records (`Idempotent-Replayed: true`) without calling the provider again; a provider that did not answer in time gives `status: unknown` (check booking-details).