For reservations in the UK, you can also contact the operating company directly, via Facebook etc. Seat reservations in the UK should be free.

For Eurostar, use this website. Do this ASAP because seats are limited. Use the pencil icon to change journey details (no. of passengers etc.). Fare is 30 EUR per person in second class.

For Brussels to Wels, use the DB Website and click on the "Seat only (no ticket)” link. Request Brussels to Wels in one go because here, you pay just 4 EUR per journey (and person), even if multiple trains are included. Reservation is optional here.

@mpierson  as @rvdborgt  suggest especially Eurostar is often sold out as they still operate less trains than usual. And avoid the Thalys after brussels and catch the ICE  as suggested. 

Hi @seewulf and @rvdborgt  - Thanks so much for your responses. A few follow up questions: 

1. I’m on the Eurostar website and don’t see my train listed as an option, does this mean the train is sold out? In which case, should I cancel my travel day and rebook, checking availability on the Eurostar website and the websites of all the train systems I’m using first before adding it on my Rail Planner app? 
2. When I clicked on the link to the Eurostar website you provided, the purchase price came to 130 Euros. How do I tell Eurostar I’m only reserving a seat, not buying a full price ticket? Is there a place to input a number associated with my Eurail pass? 

Thanks so much! 

1. When a train is missing, the pass fares for it are probably sold out indeed. On Tuesday the 26th, there are already more options.
2. The link I gave is for supplements specifically. When I click it, I still see a 30 EUR fare for the one train that appears on the 25th. What exactly did you change/do before the price went to 130 EUR?

As to adding a train or a travel day in the app: I basically only do that when I'm sure I'm going to take that train, which is often just minutes before I board it. Especially with travel days you have to be careful: you cannot cancel them anymore if that day has already started.

The €130 price comes up when I click to purchase the supplement through the link you sent. It’ll read as €30 until I hit “purchase” and the price jumps to €130. Is there another way to reserve the seat? And regarding using a travel day, are you able to reserve seats before getting the ticket via the Eurail app? 

Damn, i've now also seen it. Eurostar seem to have done something to their website to block booking a pass fare there :(

Booking a Eurostar pass fare is also possible here:

https://www.b-europe.com/EN/Kopen/Pass#TravelWish

But there's an extra charge of 4 EUR per booking.

Making reservations is entirely separate from your pass. Reservations don't show up in the app and activating a travel day (or not) has no influence whatsoever on your ability to book a seat.

So I found where to purchase the seat for Eurostar but now in spite of logging in, the Eurail / Interrail website won’t let me add my actual billing address to the site to pay (I’m from the US and the billing address country options are only European). So now that I’ve found out how to buy the thing, I can’t. 

I’ll reach out to Customer Service for Eurail / Interrail. 

Since you're from the US, you will need a Eurail pass. Maybe you were trying to buy an Interrail?

I’ve been pretty careful about that, since I know folks can get snagged by accidentally buying the incorrect pass. I even double checked my profile and it confirmed I’ve got a Eurail pass. Not sure what’s up. 

OK! I cleared my cache and cookies and whatnot and managed to successfully book for my Eurail pass. Whew! I’ve got my tickets and am feeling good. Per your suggestion, I’ll get my travel day set up closer to time on the Eurail app. 

Thanks so much for all your help @rvdborgt  - you’ve been a rockstar. 

Best,

Meg