I'm trying to make a seat reservation for the TGV 6035 from Paris Gare de Lyon to Nice Ville at 19:08-00:46 on 22/07. The Eurail website says that prices are unavailable for this train.
If I try to book through travel.b-europe.com instead, there are still some available seats. However, in order to book my seat, the website requests a Pass Cover number in the "Ticket Details" section. Since I have a mobile Eurail pass, I do not have a Pass Cover number and am unable to complete the reservation.
How can I receive a Pass Cover Number? Is there an alternative way to book a seat on this train?