For which train were the reservations sold out ? It's rare 1 month in advance but it can happen (Thalys and Eurostars have quotas for example).

Rail Planner isn't updated often (bad tool for planning, use bahn.com) but the prices should be correct if you make the reservation through interrail.eu (incl. 2€ booking fee). However there are often better and cheaper ways to make them. Have a look at : https://www.seat61.com/interrail-and-eurail-reservations.htm

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

Optional reservations : heavily depends on the route. From not needed in Switzerland to very much recommended on ICE trains in summer (esp. cross-border route to Belgium). Most do not cost much : 3€ through tickets.oebb.at. If you'd like precise advice, give us the route and we'll gladly help.

On the other hand some trains do not offer seat reservations at all : trains in Belgium, the Netherlands or regional trains in general.

Here are the possible options for Spanish trains : https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105/index2.html?postid=18419#post18419

If you happen to visit Germany or Switzerland during your trip…

To cross the border into Spain : Euskotren every 30 min between Hendaye and San Sebastian (not included, 3-4€). But I think you might already know that.

Thank you so much for useful information. I am only briefing changing trains in Germany on my way to Spain, so I am not sure I’ll have the time to try to book the seat at the RENFE train there by DB counter, but now I know this is an option :)

It was København-Hamburg where seats were sold out (at several times too), but I manage to get an alternative route …

It is true that this route is incredibly popular as it is the most direct link to Scandinavia. Fortunately there's most capacity since yesterday through German IC carriages (instead of small Danish units).

Did you check availability here ? https://travel.b-europe.com/dsb-rail/en/reservation-only#TravelWish -> the best website for overview but the best place to book is cd.cz : 72 CZK or about 3€.

Yep there are alternatives but not many…

Hopefully you'll have time at a DB ticket counter but queues can get quite long... prepare a sheet with Spanish train numbers because that is the way staff can book them (although they may not all be aware of the option).

Thanks again. I checked both DSB and DB, in addition to Interrail website. All three suggest there are no more seats available. Thanks for the suggestion about cd.cz and recommendations about reservations at counters. 

There are alternatives if you look for journeys via Flensburg or via Niebüll.

Yes, I had noted Flensburg as an option, but did not know about Niebuell. Thanks! 

Hi again, I did find a seat on a night train connection from Copenhagen to Hamburg (IC399) leaving at 23:52 and arriving at 06:26, but I found it on the Deutsche Bahn website. The interrail planner does not show this train on the date I am interested in travelling. From other chats, my guess is that the Interrail planner is not fully updated and that this is the reason why this train doesn’t show up, but as far as I understand all IC should be ok? I have also read in the FAQs that I can manually add train connections that do not show up on the Interrail planner. I cannot see this option yet (I guess this is because my pass is not activated yet). Do you have any experiences with this manual adding of journeys? Do I add them under ‘My trip’ or under ‘My pass’? Thanks :)

You didn't mention your travel date.

If this is the departure on 30 June, then please update your app because the 23:52 departure from Copenhagen is in it. In any case, you can travel on it.

To add a train manually, scroll down in the results of the planner and then tap on "Add it manually”.

Thank you! I had overseen this option at the bottom. And no, the train is not in the Interrail planner for the date I am interested in (2nd July). 

Indeed. If the train is still not in the app on your travel day, then just add it manually.