Hi! I'm travelling from Utrecht Centraal to Budapest in november and for my final train, from Vienna to Budapest, the website says I can't book a seat reservation. It says the prices are unavailable. Does anyone knows how this works? 1) Is it full? 2) Can I not book it in advance but is there still a chance I can take the train? 3) If I book a seat reservation on the site on this train company (https://www.cd.cz/en/), can I use that reservation to travel with my Interrail pass? On the website I have the option to book a ‘reservation only’, but will that allow me to hop on the train with my pass (and thus not pay the ticket)? Also, if I try to make this reservation the site says the train is temporarily unavailable.
In at least one of the trains that are part of my journey (also if I switch to a different date) I have this problem.
Also I was wondering in general if a certain train says ‘reservation not required’ but you can optionally book it, how this works. Is there then a possibility you can't take the train if you haven't booked? Or can you just always take the train but no guarantee of a seat?
Thank you!