How do we add excess baggage to itinerary?
The service named AncillaryPriceRQ can be used to shop for air extras (additional products, including extra baggage) to be sold in addition to the flight tickets:
https://developer.sabre.com/docs/soap_apis/air/book/air_extras
Then, in order to add the item to the itinerary, the service UpdateReservationRQ can be used:
https://developer.sabre.com/docs/read/soap_apis/management/itinerary/update_itinerary