Retrieve the current order and confirm the ticket status is open/active (coupon status O) before attempting any seat or ancillary modification.
Call the NDC ServiceList endpoint (or Sabre's Seats NDC plugin) with the order reference to retrieve available post-ticketing ancillary offers, filtering for seat upgrades on the relevant flight segment.
Submit an OrderChange request with the selected ancillary offer ID; include the payment element for the upgrade charge and the SSR data for the new seat assignment.
On OrderChangeRS success, note the EMD-A document number — the associated EMD is automatically issued for the ancillary and linked to the ticket coupon for that flight segment.
Update your seat assignment record in the booking data store; send the passenger a confirmation with the new seat number and EMD-A document number.
At check-in, the airport/airline system will validate the EMD-A coupon against the ticket — ensure the EMD-A number is included in any itinerary documents sent to the passenger.
Known gotchas
EMD-A issuance requires that the base ticket is already issued — attempting post-ticketing ancillary addition on a held (unticketed) booking uses a different flow (pre-ticketing ancillary selection).
Carrier business rules for post-ticketing seat modifications vary widely; some carriers only permit changes through their own NDC channel and reject intermediary modifications after a certain window.
If the OrderChange is accepted but the EMD-A coupon number is absent from the response, do not show the seat as confirmed — contact the airline or GDS support before notifying the passenger.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp