Can I add my own service fee on top of the flight fare the API gives me?

Yes, you can add your own fee on top of the fare that the flight API returns, and that is how most agencies earn on the flight sales that come through their own portal. The markup is applied before the price is displayed, so your customer sees one final amount in the search results and the same amount on the payment page, rather than the raw supplier fare with your charge appearing later.

How you set it is largely up to you. In most setups you can keep the fee as a flat amount or as a percentage, apply it per passenger or per booking, and use different rules for different airlines, routes or cabin classes, so a long haul business class sale does not carry the same fee as a short domestic hop. If you work with sub agents, you can usually keep your own margin separate from the one they add, so each party sees the price meant for them.

There are honest limits. The fare itself is controlled by the airline or the supplier, so your fee sits alongside it rather than changing it, and the airline documents your customer receives may still show the fare and taxes as the airline filed them. Some suppliers and airlines also have rules about how a service fee must be shown or invoiced, and how many different markup rules you can create can depend on your plan, so the exact arrangement varies.

The useful next step is to write down the fee you want on a typical domestic booking and a typical international one, then ask our team to confirm what your flight suppliers and your plan allow before you go live.