There are several different connections for this, including ones connecting to Ouigo TGV which are not valid with passes.

Look for a connection via Bellegarde (Ain) then book the Bellegarde - Paris section here https://travel.b-europe.com/eurail-ge/en/booking-tgv#TravelWish

That will give the €10 or €20 reservations.

The connections Geneve - Bellegarde do not require booking.

I bought a second class ticket from SNCF portal for Bordeaux to Paris for 20th Oct (TGV INOUI).

I now would like to cancel the ticket and use a Eural pass day for the above travel.

What would be the cancellation charges?

It is written that: TGV INOUI: on the day before and the day of departure, the ticket exchange/refund fee increases to €15. 

So if I cancel today, how much do I have to pay?

Thanks for the help.

https://www.sncf.com/en/itinerary-booking/exchanges-cancellations

After-sales options for Loisir tickets (Prem's, 2ⁿᵈ and 1ˢᵗ)

• up to 31 days before your train departs: you can exchange your Loisir ticket free of charge, or cancel it and get a full refund
• 2-30 days before departure: if you request an exchange or refund, you will be charged a fee of €5 per person per journey
• TGV INOUI: on the day before and the day of departure, the ticket exchange/refund fee increases to €15  
• Intercités requiring booking: on the day before and the day of departure, the exchange/refund fee increases to 40% of the ticket price, with a minimum of €5 and a maximum of €12
• starting 30 minutes before departure, you cannot exchange your ticket more than twice (same day, same journey). If you make an exchange during this period, the ticket is no longer refundable
• once the train has departed, Loisir tickets cannot be exchanged or refunded

The above suggestion I got when I tried to book Geneva to Paris seat reservation and failed each time.

Then I tried to book the Bellegarde (Ain)-Paris leg through Eurail website following the above suggestion, but the same error is coming at the last moment. The error is:

Please try to find an alternate connection. The unavailable leg will be removed from your cart.

Please help. I need to book Geneva to Paris reservation urgently for 26 Oct.

Thanks.

Works fine for me from Bellegarde - Paris Gare De Lyon through b-europe, up to the point of payment.

Not sure what else to say to you.

Here is information about the known ways to book the TGV from Geneva to Paris.

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105?postid=37042#post37042

Please be aware that the cost for the seat reservation is very high for the international travel. If you take a regional train from Geneva to the nearest station in France where the TGV stops it will be much cheaper. 

Thank you. The above information is very helpful but it stuck at

Eurail/Interrail pass cover number

I have a mobile pass. It is six character long and the website is not accepting that as a valid number.

What to do? Please help.