You probably registered the journeys in “my trip” in the app. The pass is your ticket. Best not activate the travel day (tapping the ledger on your planned trip in “my trip”), until just before boarding the train. The terminology is a bit confusing :)

When are you travelling?

Seat reservations for Eurostar can be bought via the reservation service of Eurail/Interrail or https://www.b-europe.com/EN/Booking/Pass#TravelWish and you’ll need to generate a pass cover number if you use the latter:

Best do it quickly, as reservations for Eurostar can sell out.

Best read the guide below attentively if you should want any other seat reservations for the rest of your journey:

YOu do not have anything for this €* untill you have confirmed bookings which cost extra-at least 30€. {PLUS that this forum brims with com laining Brits who are unable to get such RES (booking is too ambigue a word-avoid it) at short notice or even around main hols loger away. Best is too NOW check this b-europe for when what is available. In actual fact hardly anyone will even want to see the pass itself-its the REServation that counts and opens  gates etc!

Thanks for your reply.  We travel on 5th April and have booked the tickets on the Mobile App.  However there is no clear way of booking the reservation needed.  Wasreally hoping the process wiould be easy as we have a Two month Pass and will be making lots of jouneys,

Plenty of availability for pass holders that day, but book quickly as it will be Easter holidays in many countries :

(prices for seat reservations  on Eurostar for 2 travellers)

Reservations are a bit tricky, and annoyingly complicated sometimes. Best read this topic (linked below) if you want to reserve your trains without the interrail reservation fee.

https://community.eurail.com/train%2Dconnections%2Dreservations%2D47/how%2Dto%2Dget%2Dreservations%2D105

You need a reservation for the Eurostar and you should definitely make the reservation ASAP so that you can be sure to travel the day you plan. 

There is a limited number of pass holder seats on the Eurostar and on popular departures and during high season those sell out weeks, and sometimes months in advance.

The best place to see the availability of passholder seats and make reservations on the Eurostar is 

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

Press "later trains" and eventually you will find the next available connection. 

If you have a mobile pass you need to generate a Pass Cover Number in order to make the reservation at b-europe. You do that here in the PCN generator:

https://community.eurail.com/news-and-announcements-39/pass-cover-number-generator-is-live-5653

You should never activate the pass or a travel day in advance, certainly not if you still have to book mandatory reservations. There is no advantage in activating the pass or a travel day in advance.

Also note that activating a journey in the app does not book anything.

Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days. 

 Planning

The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries. 

 Reservations 

Unfortunately, as mentioned previously, Interrail terminology can be confusing so here is my attempt at simplifying some of it.

Firstly the App has 4 main sections, only one of which is usable as a ticket (more later).

1 - The rail planner - You can look for available trains and if suitable you can transfer to your TRIP.

2 - Your TRIP - consider this your diary for the trains you intend travelling on. You have only one TRIP per pass, even if you have more than one holiday planned with that pass. You add trains either from the planner or manually if it is not listed in the planner. Until you add them to your pass these are simply a listing and can be removed or added at any time with no consequence.
3 - The reservation tool - This is a link to an external reservation service and is just one method of getting reservations - It is a one-way system and does not link any reservations to the pass. There is plenty of advice in earlier posts.

4 - Your travel pass - To travel on a train using a mobile pass you need a valid ticket, and for some trains an accompanying but separate reservation. Your pass is the only section that becomes a valid ticket to travel, but you have to create a Travel Day and transfer all trains you travel on in that day from your TRIP.

Firstly you add  your first train of the day from your trip by activating the slider. This creates a Travel day with a QR code for the day and the train details in text below it. This is now you ticket for that train and the advice is not to do this until you are certain you are travelling that day on that train. There is nothing to be gained by doing this any sooner.

As you travel through the day you add any further trains from your TRIP to your pass, again the advice is just before you board the train. You can add and delete trains to your TRIP right up to the point of boarding.

The only extra you may need to board some trains is a separate seat reservation but the rail planner generally shows whether mandatory reservations are needed - you can always ask the community. As a point of interest if you are a dynamic planner (i.e. on the fly) reservations can be purchased in all stations of departure, but they may need sight of your pass.

Hi Thanks for this.  Its just for Eurostar I thought it would be best to book reservations well in advance.  Due to the possibility of the Train being full if we leave it to last minute.  As it is in the week running up to Easter weekend.  Cheers