You can call  b-europe and make the reservation. No need of Pass Cover Number.

The phone call is rather expensive.

https://www.b-europe.com/EN/Contact/Contact-Centre

The best way to make reservations for French trains is to call SNCF. No need of Pass Cover Number. 

https://www.sncf.com/en/customer-service/contact-us/telephone

 Press #85 for English, no booking fees, reservations are sent via e-mail

To get your Pass Cover Number, if you still will need it, you need to contact Customer Support through this form and ask for the Pass Cover Number.

https://eurail.zendesk.com/hc/en-001/requests/new

Customer Support is currently overloaded with requests so you will probably have to be patient to get help. Please let Customer Support know what date your travel will start so that they can prioritise your request correctly.

@AnnaB Thanks I will try to call SNCF tomorrow morning. I've also tried to make an account at their homepage and then tried to book tickets at https://www.sncf-connect.com/app/en-en/home/search but honestly, I have no clue where I can like ad my interrail pass and then book it from there. Everything seems actual a little complicated.. =)

You can't make reservations online with SNCF if you have an Interrail pass. SNCF have stopped to sell reservations for pass holders online.

@AnnaB okay thanks so much for your answers!! it helps a lot !!!

This account on SNCF is ONLY meant for those buying normal tickets. They will automatically remove it if not used a certian time-FR laws are strict to protect privacy and online & all that

I had this exact same issue- today in fact- for Lyon to Marseille. I ended up going to the SNCF TGV InOui help desk at Gare de Lyon Part-Dieu, and their ticket machines let you buy seat reservations using a Eurail pass as a “discount pass”. The staff their guided us through buying the ticket on the computer there, took about 5 minutes, and we got our seat reservation. First class upgrade was only 4 euros extra, so it was a total of 44 euros for 2 of us to book seat reservations on a first class TGV from Lyon Part-Dieu to Marseille Saint-Charles. And to be clear, I did book day of, but we could have booked ahead of time.

Hope that helps!

Hi @Tess Nygren !

I have the same problem! Did you end up calling https://www.sncf.com/en/customer-service/contact-us/telephone this one? Did it work?

Thanks!

@Renske Steenstra yes I called them and that was super easy just remember #85 for English. But to be fair I ended up with another problem I couldn't pay with my credit card at all over the phone. They said like America express is the best. I guess it depends which country your bank are from. Still it is definitely worth a try to call them ! 

@Tess Nygren thanks so much for your quick reply! It worked out. I wish you happy travels 

Some user in this community said that asking Interrail via Social Media you get very quickly the Cover Pass Number for using it to buy reservations online via B-Europe. 

You can now generate your own PCN.

In addition, NS can also book TGVs without booking fees (since pass reservations are not available on their website) and they're less picky about credit cards than SNCF.

Thanks so much. I was able to generate my pass cover number using this link

The answer above on “generating our paper pass number” through that link literally made my day! It worked perfectly for us. And because of that, we could book (seat reservation) TGV train on 1st class seats even though we have a 2nd class Eurail Global Pass for a small fee (5 euro per person).

So, thank you! 

Does this really work ?

Sure it does.