I’m gonna check. But as always, we need details. Which trains are you trying to book? Where are you trying to get seat reservations? From where to where, which date?

With a first class pass, you can book second class seats when you’lld like. Not the other way around.

Sleeper trains don’t know 1st and 2nd class in general. But you have a seat coach, couchette (4 or 6 bunks) or a sleeper car. You should be able to book any of those types, no matter the class of your pass.

Sorry for the missing details. It the train from UTRECHT CENTRAAL (Netherlands) to NUERNBERG HBF (Germany) on 16-08-2023 20:03 train NJ 40421.

Here you see the problem:

If I then try to book I get this:

Try via öbb nightjet’s website: https://www.nightjet.com/en/#/home

Seats, couchette and sleeper are all still available.

Note that these trains are often delayed, and your 36 min connection is quite sure to fail. Where do you want to go in the end?

Please use nightjet.com to book this train. That's less buggy and cheaper. Add the Interrail/Eurail discount for each person.

Thank you both for the advise!

I want to go to WIEN HUETTELDORF (Austria) in the end. 

what can you recommend to do?

You could book directly to Vienna Hbf on the same train via Nightjet. Unfortunately no couchettes or sleeper cars are available…

Personally, I never take seats on night trains. I just won’t be able to sleep. Waking up in the middle of the night to change trains, is also not a good option imho. I would book until München maybe Innsbruck, and continue by day trains to Vienna. Than you get a long night’s sleep at least :)

I'd indeed continue tow Munich or Rosenheim and then change to Vienna. It will take a bit longer but you'll have more sleep.