Construct and price a multi-city (3+ slice) flight itinerary using Duffel's Offer Requests API.

Steps

1. Call POST /air/offer_requests with a slices array containing one object per leg (each with origin, destination, departure_date) — e.g. three slices for LON to JFK, NYC to SFO, and SFO to LON on different dates; Duffel treats any offer request with more than two slices as multi-city.
2. Add the required passengers array (by type or age) and optionally cabin_class and max_connections (0 for direct-only legs) to the same request body.
3. Optionally set the supplier_timeout query parameter (2,000-60,000ms, default 20,000) to control how long Duffel waits on slow airline searches, and return_offers=false if you'd rather page through results via the List Offers endpoint.
4. Inspect the returned offers — each contains all of your slices in order, with each slice broken into one or more segments — and pick the offer whose combination of segments/price fits.
5. Before booking, call GET /air/offers/{offer_id} to get the latest price for the chosen offer and confirm expires_at is still in the future.
6. Call POST /air/orders with the selected offer's id and full passenger/payment details to book the multi-city itinerary.