For now it only works on the desktop version of the website, not mobile nor on the app.

At the start you click on Add rail pass and select Interrail Global Pass 2nd class (or 1st class). Then you search the train you’d like and reservation prices will appear.

Let us know if it doesn’t work. I’m about to use the website tonight too for the first time. :)

The Rail Europe app can't book pass reservations (yet).

Their website can but you need to use it on a pc. On a phone, you won’t see "Add rail pass”.

Thanks-so it only works on the desktop version of the website. 
This seems to work -https://www.browserstack.com/guide/request-desktop-site-on-iphone

and Interrail pass is then available on my iPhone

Thanks for the URL! A similar things also exists for Chrome on Android:

https://www.browserstack.com/guide/view-desktop-sites-on-android

I have been looking on Rail Europe for trains - and the information is different on this website than on the interrail app. 

Train from Bruxelles-midi to Koeln Hbf 24th July 2024 16.23 arr 18.15. I am struggling to get a Eurostar seat booking for this. So trains without seat bookings:

On the interrail it states you go to Liege-Guillemins with ICE 317 first, and then to AachenHbf and then Koeln Hbf

on Rail Europe ICE 317 is a direct train to Koeln Hbf and I do not need a seat reservation.

Do you know which is correct??? Very different trains?