Did you select a trip in the reservation module?

For Norway, by the way, Interrail can only supply paper reservations, with an added cost of 9€ on top of the 2€ booking fee and the actual reservation. It's better to call Entur; they will send reservations by email. See this page (scroll down to Norway).

Hello Dina

1.Are you trying to making reservations via website or via the app?

2. Please check you have latest app installed, are you using Android/ IPhone?

3. Please provide snapshots of the error you are getting? 

IF you are some time in NO you can -easy peasy- simply go to a counter-though very few are still open, only in the big main cities-and have them arrange it for you. Note that other as the site tells, you since a year or 2 MUST REServe every trip on long-distance and this also cost money. For sleepers in overnight trains it seems there are as for now still restrictions on not sharing with strangers due to covid-this may change any day.

I am using Android. I think I have the latest app (I just installed it a few days ago). And I am trying to make the reservation via the website. (After I have first checked in the app  if this trip is possible). 

And on the website it says: you have no trip.

Then I'd say add a new trip on the website with your pass details.

For reservations in Norway though, see my earlier comment.

Thank you for your answer. I tried to phone Entur. But the waiting time was too long.

I have to try it again.

I have succeeded in phoning to Entur. And I could make my reservations!!!

Thank you for your help and support.