trains no reservation possible

Are you talking about a train with limited Passholder reservations? ( Eurostar for example) 

Also you doont have to purchase the reservations via the interrail website (which adds a 2€ booking charge per reservation on top of the reservation price. There is this guide for where to best get reservations without additional booking fees https://www.seat61.com/interrail-and-eurail-reservations.htm

​@Rachelarts99 If you mention the train and date you are having trouble with it would be easier to give you relevant tips.

For instance, I want to book a train from Amsterdam to Paris/Marseille, but it says: ‘No price results were found. Pass holder reservations may be sold out for this connection, but there are other ways to check for available seats—more info below our timetable.’ - very vague and quite insane since almost all tracks state this the days around the 23th for me. 

Also, I want to book a train from Paris to Marseille on Thursday the 23th of April 2026. But the site says the tickets are not for sale: ‘Prices for this journey will start to be available {days} days before departure’.

Why then did I buy an interrail ticket if I can't actually buy train tickets .. 

So regarding the Eurostar from Amsterdam to Paris it looks like most of the eurostar trains in the morning have no available pass holder reservations. But later that day or on the afternoon 22. April there are Passs holder reservations available. 

Its mostly just eurostar with the limited Pass holder reservations. (which is why i usually avoid them and their high reservation cost)

Regarding the TGV reservation from Paris i would recommend to buy it via raileurope.com and not on the interrail reservation website if you have a normal interrail pass (not the plus pass)

Those seem to be already available and start at 10€ if atrain is mostly booked out, they change to 20€.