Can my customers choose business class or premium economy when they search for flights on my portal?

Yes, your customers can search by cabin class, and most flight booking APIs accept economy, premium economy, business and first as part of the search request.

In practice this means the cabin choice sits on your search form alongside the dates and the passenger numbers, and the results come back priced for the cabin that was asked for. On the booking screen you can usually see which cabin each leg of the journey is in, so your agent can confirm it before the ticket is issued. The level of detail does vary by supplier, so some responses give you a plain cabin name while others also include the booking class letter the airline uses internally.

There are a few honest limits worth knowing. Premium economy is not offered by every airline, and some suppliers group it in with economy, so a search may return fewer options than your customer expects. On a journey with connections the cabin can differ between legs, for example business on the long sector and economy on a short feeder flight, and how clearly that is shown depends on the supplier data. Low cost carriers usually have a single cabin with paid extras rather than a true business class, and upgrades requested after booking are handled by the airline rather than through the API.

The sensible next step is to run test searches on the routes you sell most and see which cabins your connected suppliers actually return, then decide whether to show every cabin option on your search form or only the ones that reliably bring back results.