Can my customer add their frequent flyer number when they book a flight on my portal?

Yes, in most cases they can. The passenger details screen on a flight booking can carry a frequent flyer or loyalty number along with the name, date of birth and contact details, and that number is passed to the airline with the rest of the booking. If the airline accepts it, the miles are credited to your customer's account just as they would be if the customer had booked on the airline's own website.

What makes it work is the name matching the loyalty account. Airlines check the passenger name against the name held on the membership, and if the spelling is different, or the surname and given name are the wrong way round, the number is quietly ignored and no miles appear. The field is only as good as the care your staff take typing it in, so ask your customer for the name as it appears on their loyalty card.

Be aware that this is not guaranteed for every airline or every fare. Some low cost carriers do not run a loyalty programme at all, some airlines accept the number but do not award miles on the cheapest or heavily discounted fare types, and a few suppliers do not pass the field through to the airline at all. Whether the number can be sent depends on the airline, the fare and the supplier connection, so it is not something we can promise across the board.

The practical step is to test a live booking with a real loyalty number on the airlines you sell most and see whether it shows on the ticket. Where it is not accepted, tell your customer they can still add the number at check in or claim the miles from the airline afterwards with a copy of their ticket.