Can I tell whether a hotel room is confirmed straight away or only on request before I take my customer's money?

Yes, in most cases you can see this before your customer pays. A hotel booking API normally sends back a status on each room option that says whether the booking is confirmed the moment you make it, or whether the request has to go to the hotel and wait for a reply. That status can be shown on your portal as a plain line next to the room, so your staff and your customer know what they are buying rather than finding out afterwards.

The wording is not the same for every supplier. Some call it instant confirmation, some call it on request, and some send back a short code that has to be read and turned into ordinary language on your side. Whether the flag comes through at all, and how reliable it is, depends on the supplier and on what their API actually includes, so it is worth checking this supplier by supplier instead of assuming they all behave the same way.

When a room is on request, the booking sits in a waiting state until the hotel answers, which can take a few hours and sometimes longer. You will need to decide what happens to the money in the meantime, whether you hold the payment and only charge once the hotel says yes, or take it and refund if the room is turned down. What you are able to do there depends on your payment gateway and on your plan, so it is not something to promise a customer before you have checked it.

Ask each of your hotel suppliers which booking statuses their API returns and how long on request rooms usually take to be answered, then decide how you want those rooms shown and paid for on your portal.