Reservations for the TGVs from France to Spain can also be bought from Belgian, French and German railways and possibly others. The best is to book as soon as possible because the quota can be full if you wait too long. Have you asked at anItalian railways ticket office?

I can't do that online?

Maybe, if you manage to get the reservation tool on the Interrail website or app working. But it will still be issued on paper and sent to you via the post for a total of 11 EUR in extra fees. So if you have a ticket office near you that can do international reservations, that may be quicker and cheaper.

So there aren't existing E-Tickets for that?

Apparently not. I have booked normal e-tickets for these trains (without Interrail) but the Interrail supplements don't seem to exist (yet) as e-tickets. I recently read somebody managed to make a reservation for one of these trains through the Interrail website and it had to be sent through the post.

As @rvdborgt  said there is no way of getting E- Reservations for that Route and i recommend to reserve well in advance as the actual the timetable is reduced and the seats for Railpassholders are limited. As Backup you maybe take a train to Perpignan and then via Cerbere/Portbou further to Barcelona (nice route along the Coast but takes quite alot time)

So it's to late if I buy the ticket one day before the departure day?

I wouldn't risk that.

The Problem is only that I don't know if it's possible to go to spain in two weeks (because of Covid)

And so, it's a risk to buy that reservation

Yeah the there is nothing sure in this pandemic Because of that maybe consider to take the back up Route as you need with luck no reservation or just a domestic one within France :)

BothBelgian railways and German railways refund 90% if requested before departure (for this particular reservation). Other railways/points of sale may have something similar. Just ask before paying.

Oh, I've seen at the moment, that I can order my Paper-Ticket from Nimes to Barcelona online. Am I right there? Can anyone check that, because I don't have any experience with seat place reservations.

The train starts at 11:24 am on 10th July at Marseille St. Charles to Nimes, and at Nimes I take the train at 1:14 Pm to Barcelona.

Am I right there that I can buy both of them at the railplanner app, but marseille - nimes is an e-pass and nimes - Barcelona is a paper pass

That is correct.

Marseille - Nîmes (or Perpignan, which is the last station in France) is available as an e-ticket and Interrail charges a 2 EUR fee per seat for that.

From France to Spain it will be a paper reservation and Interrail will charge a 2 EUR fee per seat and a 9 EUR postage fee per order.

Like I said: it may be quicker and cheaper to go to a ticket office near you.

Okay, and what I ask at the ticket office?

I need a seat reservation only for my interrail trip, from a to b?

Indeed. The best is to make a print of the timetable, on which you can see the stations, times and train numbers.

Okay, thanks a lot, I try