Hi Tarun, I provided you with a number and issuer details by replying to your private message. I trust it is solved now. If not, do not hesitate to reach out. 

Hi! 

I have a similar problem. I bought the Interrail France ticket and wanted to book seat reservations for my train from Paris Gare de Lyon to Avignon (TGV). However, I can’t make any reservations as my pass cover reference is incorrect / invalid.

Could you kindly help me out? Thanks!

Biljana

Do you have a mobile pass, in that case you don't have a pass cover number. I guess that you are trying to make reservations for French trains through b-europe.

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.