you click for only seat to get a reservation for trains that have optional reservation rule. Like RJX, RJ, ICE, EC, IC (with exceptions when the train have compulsory reservations)

For trains with compulsory reservation like Nightjet or Frecciarossa and IC in Italy you go to one way ticket and choose at adult the discount Interrail/Eurail Global Pass. 

Thanks for your reply.
So, If i want to book a IC train from Basel to Utrecht i only have to buy a ‘seat only reservation’? And where can I see when the trains have compulsory reservations?

All the best,

Tom 

Hey, yes for the IC train (you mean the seat car part of the Nightjet nightrain Amsterdam-Zurich?) and also on the same route the ICE you can reserve via seat only option via ÖBB tickets.oebb.at 3€/seat/train or via bahn.com with the seat only option (with seat plan 4,50€/seat/journey)

If a train have compulsory reservation or not, you see it in the railplanner app and also on the planer of like bahn.com. Often it says reservation compulsory. In Italy this is missing, but you can see that the train has compulsory reservation with the note “Global Price”, which only trains with compulsory reservation have. 

The ONLY portion of train that has mandatory RES on this line is that NightJet-which you incorrectly label as OeBB (Oesterreichische BundesBahnen), thats the sleeper/couchette section. This overnight train also has  a few seats-only cars by DB-these are optional REServation (and strangely enough cannot be done usual way on DB/seat only, but has to be done via OeBB site-and as noone knows, hardly anyone does).The many more normal daytime trains are mostly ICE, run his-peed and only 1 of these goes into NL (if at all-it seems to be often cancelled lately due to not enough stock able to run)

Ahh I see. So the nightJet is a train compartment in the IC, right?

And are you saying that most of the times people don’t reserve the seat only? Or am i understanding that wrong?

All the best

It can also be done via DB. Please check before you write.