Can I sell a trip that goes to more than one city on the same flight booking?

Yes, most flight booking APIs let you sell a journey that covers more than one city on a single booking, and this is usually called a multi city search. Instead of one outbound flight and one return, you set out each leg with its own from, to and date, and the API prices the whole journey together. Your customer normally ends up with one itinerary and one ticket, which is easier for them at check in and easier for you to manage afterwards.

How well it works depends on the supplier behind the search. Full service airlines and the larger content sources handle multi city journeys comfortably, and they will often price the whole trip more cheaply than the same legs bought separately. Low cost airlines usually do not, because they sell each flight on its own, so a journey that mixes them may come back as separate bookings with separate references and separate rules. Some sources also limit how many legs you can put into one search.

There are a couple of things worth knowing before you promise a customer anything. If all the legs sit on one ticket, a change or a cancellation normally applies to the whole journey and not just the leg your customer wants to move, and the strictest fare rule in the itinerary tends to apply to the lot. If the legs come back as separate bookings, a delay on the first flight is your customer's problem rather than the airline's, so leave a sensible gap between arriving and departing.

Try a few real multi city routes in your test environment and see what each of your suppliers actually returns, then decide whether to offer it openly on your website or keep it for enquiries you handle yourself.