Don't book that train via Interrail; that's a waste of money.
Reservation is optional but if you want a reservation, you can book it for 76 CZK (~3€) via Czech railways. Look for the connection, then click on "I want a reservation only”. You'll receive it via e-mail.
Can someone explain to me why these €9 are mandatory and what they are for? Once I pay and reserve the seat, how will I receive the reservation ticket and the seat number?
The 9 EUR is the shipping cost for sending the ticket to you with registered mail. As @rvdborgt says above. Don't book this through the Interrail website.
As said above don´t reserve via Interrail/Eurail itself
Reserve via Czech Rail, Austrian Rail online or a at international ticket office (in e.g. Germany,Austria,Czech Republic)
Ok thank you very much I will do that.
Finally, how can I find out which trains require seat reservations to get on the train? Are the trains that appear with compulsory seat reservation on the Interrail website correct? Can I buy the seats at the station before boarding the train?
Again-it has been told here so man times-and also to you before, so I hope you can read: do NOT rely on this planner app-use a decent one, best is bahn.com (german railways) covers even slightly more as app and very clearly tells If a REServ is mandatory, optional or not possible per train that appears in the search/overveiw. Cd.cz=czech railways has about the same, but the language may sometimes turn to czech only.
It will also show a seat only option to REServe right away-but that will only work for german trains (local and to/fro)
I've been looking on the Czech Republic train website and I can't pay in euros. Can I buy the seat reservation ticket at the station where the train leaves?
Can I make all seat reservations at the stations hours before the train leaves?
Czech railways charge in CZK. That should not be a problem for any credit card.
You can book this train at many ticket offices, not only in Czechia but also in Austria, Germany, Switzerland, Slovakia, etc.
Ok, so I don't make any seat reservations for now until I get to each city and go to the station. If I haven't reserved a seat on the trains that have a mandatory reservation, they won't let me get on the train, right?
If I have a ticket for a train with compulsory reservation but I haven't reserved the seat yet because I will do it the same day the train leaves, can it happen that all the seats are already occupied and they won't let me get on the train? I don't know if I explained myself
If I have a ticket for a train with compulsory reservation but I haven't reserved the seat yet because I will do it the same day the train leaves, can it happen that all the seats are already occupied and they won't let me get on the train? I don't know if I explained myself
It can always happen that a train is fully booked. And when reservations for that train are mandatory, that means you can't get on the train.
How big the risk of “fully booked” is very much depends on the train and the day.
I've been looking on the Czech Republic train website and I can't pay in euros. Can I buy the seat reservation ticket at the station where the train leaves?
The currency doesn't matter when you pay with your credit card. It should be no problem paying in CZK.