Execute a full search-to-order flight booking flow with Duffel

Verified steps

1. Authenticate by including the header Duffel-Version (current stable version string, e.g. 'v2') and Authorization: Bearer <live_or_test_token> on every request to https://api.duffel.com.
2. Create an offer request: POST /air/offer_requests with data.slices[] (origin, destination, departure_date), data.passengers[] (type: 'adult'|'child'|'infant_without_seat'), and data.cabin_class; set return_offers: true to get offers inline or poll GET /air/offer_requests/{id} until done.
3. Each offer in data.offers[] has a unique id, total_amount, total_currency, slices[], and expires_at — record expires_at; you must convert the offer to an order before that timestamp.
4. Optionally call GET /air/offers/{offer_id}?return_available_services=true to fetch ancillary services (seat selection, bags) before ordering.
5. Create the order: POST /air/orders with data.selected_offers: [offer_id], data.passengers[] (full name, date_of_birth, gender, email, phone, identity_documents[] for international), and data.payments[] specifying type 'balance' (Duffel balance) or 'arc_bsp_cash'.
6. On success you receive an order object with id, booking_reference (the airline PNR visible to airport staff), and documents[] if ticketing was instant; poll GET /air/orders/{id} until documents are present for carriers that ticket asynchronously.