Can I add my own service fee to the flight prices that come through your API?

Yes, you can normally add your own service fee or markup to the flight prices that come back through a flight booking API, and this is usually one of the first things set up when a portal goes live. The idea is that the API gives you the fare it received from the supplier, your markup rule is applied on top, and your portal or your staff screen shows only the selling price to the customer.

How flexible this is depends on your plan and on how you want to work. Rules can often be set as a flat amount per passenger, per ticket or as a percentage, and many agencies like to vary them by airline, by route, by cabin or by which agent login made the booking, so corporate customers and walk in customers can be treated differently. If you prefer, you can take the raw fare from the API and apply your own calculation in your own system instead, which gives you complete control but means you look after the logic yourself.

The honest limits are worth knowing before you plan your pricing. Some airlines and some fare types restrict what can be added into the ticketed fare, so your fee may have to sit as a separate service charge rather than inside the airline amount. That also means the figure printed on the airline ticket will not always match what your customer paid you, and a curious customer may notice. Refund and void rules usually apply to the airline part only, so you decide your own policy on whether your fee is refundable.

Before you go live, check which markup options your plan supports and agree how your service fee will appear on the invoice and itinerary your customer receives.