Difficult to say. It's tourist low season but this train has a limited quota for Interrail seats. There are more places where you can buy it. When and where is your arrival in Europe?

Interrail is all about spontaneous travelling. Try to book the reservation in the train station or if the online reservation works for you (it didnt work for me) online without a paper ticket.

If you travel in North-Italy too, there you can do most distances by regional train.

@Albrecht  The TGV/AVE Spain-France has only paper reservations! And there are only 2 trains/day to France and 2 to Barcelona. 

@Erin Graber If you get to Europe like in Germany, Belgium or France. You can also buy in the ticket offices there a reservation. (Please note that in Germany it`s possible to book it at every ticket desk, but you need at the desk someone that know how it works → in bigger stations you should get one) 

Eurail Aid Offices | Eurail.com 

Side note: I do wonder why this is still the case for pass supplements, when at the same time all other fares for this train are available as an e-ticket (and have been for a few years now)...

@rvdborgt @Angelo I will be arriving in Rome on November 18. Looking at that link about the Eurail Aid Offices, it looks like the Rome Termini station has some locations. Do you think it would be possible to get a reservation there? We go to Austria after Rome, and then to Paris, where I would try to book the reservation as soon as we arrive in Paris (2 days before we leave for Barcelona).

Thank you all for the helpful responses. It is hard to know how to approach the reservations since many resources say to book as far in advance as possible, but that is simply not possible for some countries right now (such as Spain) where you aren’t even able to get a reservation online. 

I’m not sure (Trenitalia aItaly] and the French rail carrier SNCF hate each other), but it could be possible, I would try at every ticket office. Best one would be a Ticket Office that can sell train tickets of SNCF (France), RENFE (Spain) or the German Rail (DB). DB has ticket offices also in Milan, Verona and Bolzano (in Italy).

@Angelo good to know! Worst case scenario we found an overnight bus to take instead if all the reservations are gone. Thanks for your help!

In every country, the situation is different. If you don't succeed in Italy, then do try in Austria next.

@Erin Graber Worst case scenario is to take a train that stops at every station to the french/spanish border and from there change to the next train to Barcelona. (this variant is possible without reservation)

I have a similar problem. I purchased a paper reservation online for the Paris-Barcelona train (electronic version is apparently unavailable) on December 13, 2021. It was sent out from the Netherlands on December 15, 2021 with a company called PostNL from the Netherlands. I cannot get an update as to when it will arrive in Oceanside, California because PostNL requires a zip code, but a US zip code apparently will not work on the PostNL website. To make matters worse, Eurail said that I must sign for the delivery. I have a tracking number, but that only says that the reservation parcel was picked up on December 15th by PostNL. I sent an email to Eurail (customerservice@eurail.com), asking about the status of the package and explained about the zip code problem for PostNL updates, but they have not answered. I am concerned that it may never arrive and if it does, what if I am not at home to sign for it. What a ridiculous way to run a company! I purchased a Global Pass and I regret it so far! If I do not receive the reservation by the end of January, I will contact my credit card company and request a refund for the reservation. Hopefully, they will be able to get me reimbursed.

The sender is responsible for getting this reservation to you, provided your address is correct of course. Should there be any problem, then Eurail should reimburse any extra costs. But I suppose they will reply soon.

Hi, did you your ticket come? what did you do?