Eurail is just a ticket that many, many different railway companies accept, some of them grudgingly.

The different railways have different operating methods, not only between each other but also with their own different train classes.

When it comes to ticketing and reservations; some insist on all passengers booking seats while others allow both reserved and unreserved on the same trains and a huge amount of trains across the continent do not offer reservations at all.

Unfortunately while a Eurail pass is valid across most trains in participating countries the method and cost of obtaining reservations varies considerably.

Firstly the pass/app does not include any means for reserving seats.

The eurail website has a reservation system https://www.eurail.com/en/book-reservations#/ you need to log in and add all passes to this to book seats, these usually get delivered as PDF to show on your phone or print out at home but be careful as some can only be provided as actual printed tickets posted to your residence which need to be ordered well in advance.

Alternatives are available for many companies/countries, either through the operating railways themselves or a third party issuer. A well researched description of these sources, many of which are preferable than the eurail system, is here

The most common point on this forum, even more from those wide over the ocean, is that they are way too EARly to book/reserve seats in trains. The common leeway used to be 2 month advance and here and there it is now a little longer. Thus this means that for summer/main season its by now too early. Trains are not planes and there is not a single train that is fully booked that long advance-but in some very populair nighttrains Some specific classes/private sleeper, of which there are maybe only 1 or 2 in the whole train, can get snapped up. Prob is that many unaware of how trains work then get confused. You are not competing for some very lowest priced airtickets.

As above EUrail does not own or run any trains-its valid in 33 countries with a 100+ different companies and all have their own ways of doing it. Which for some is a big attraction of EUR compared to cookie-stdd allthesame in NAFTA. But also causes confusion and anxiety.

Also quite often people think they have to RES each and every trip-it is very often not needed and there may well be other ways-using slower regional trains to avoid it-and you get that bonus of ´local encounters´-but it also often seems that each newbee only wants to use those trains that are hardest to RES etc. This €* to/fro LON is one of them.

Thank you for your responses, they have been very helpful.

For what route, date and time are you trying to make a reservation?