You’re far too early for September. They’re currently open for bookings up to July.

The trains you see on Raileurope are the slower Intercity trains. You don’t need a reservation on these anyway

what is confusing about this is that I’ve made a booking for september already for London to Brussels and there are other dates later in september showing as available?? This is on the eurostar website. I’m finding the Interrail app very poor in terms of the search results.

The London arm of Eurostar is a different operation. It only merged with the ‘Continental Eurostar’ (formerly Thalys) quite recently, so they still have different operations and put trains on sale at different times. They also have very different classes, policies, and there are check in requirements for the London one.

Yes, the Eurail app is poor. Avoid if you can! Search timetables on www.bahn.com and buy your reservations from elsewhere.

cheers. thanks for the info.