ModifyReservation() allows changing an existing reservation to include a specific itinerary for a specific unit or unit group, instead of the itinerary and unit or unit group that it currently includes. ModifyReservation() supports POST with a JSON request body that details the reservation and guest. Note that credit card information is not currently supported by the Reservation end points and payment must be collected in accordance with the agreement made with the property. You may only modify reservations that you created.