Groupon Initiated Cancellations

This endpoint is used to notify your system of Groupon initiated cancellations. The state of the requested bookings should be transitioned to cancelled. This endpoint should behave in a transactional manner, that is, if any booking in the request can't be transitioned to cancelled the whole request should fail with error code BOOKING_NOT_CANCELLABLE, and no state transition should happen to any of the bookings.