Can I add my customer's frequent flyer number to a flight booking through my API?

Yes, in most cases you can add a frequent flyer number when you make a flight booking, but whether the airline actually accepts it and credits the miles depends on the airline and on the supplier the fare comes from.

In the passenger details part of the booking, alongside the name and date of birth, there is normally a place to choose the airline loyalty programme and type in the membership number. That detail is passed through with the rest of the booking and sits on the airline record, so the airline can match it to the member's account. You can usually add a number for each traveller on the booking, not just the lead passenger.

There are real limits worth knowing. Airlines check the number against their own member records, so if the name on the ticket does not match the name on the loyalty account, the number is often ignored without any error being shown to you. Some low cost carriers run their own schemes that work differently, and certain negotiated or consolidator fares either will not take a loyalty number or will take it and earn nothing. Earning rules, tier credit and benefits such as extra baggage or priority boarding are decided entirely by the airline, so we cannot tell you in advance how much will be credited or whether a perk will be honoured at the airport.

It is worth checking in your own portal whether the loyalty field appears for the airlines you sell most often, and telling your customers to keep their ticket number and boarding pass so they can claim any missing miles directly with the airline later.