Very hard to say without further exact details.

Its most often better to simply use the local train company site, f.e. DB=bahn for Germany, SJ for Sweden etc. These allow to make REServations without also buying tickets. Seewulf, a very helpful other frequent responder has made several instructive items about that how to do

MAJOr porblems are very often reported on this forum for French/SNCF TGV-trains, even more for trips to/from FRance from other countries-in short, this is not possible online. Somehoiw it appears that each and everyone wants to use the Barcelona-Paris 1/day TGV.

Or perhaps you chose a trip that does not even need a REServation-again, without details impossible to say

Please let us know which connection you were looking for on which date and time.

Hello, I was looking for a Bordeaux-Paris train during the day of December 17th. And for trains without reservations, the simple flash code of the "rail planner" application is sufficient to board the train?

If you don't see any trains Bordeaux - Paris for 17 December in the rail planner app, then please download the latest app update and try again.

For a train that does not require a reservation, you need to add it to your trip and the to your pass, which will generate a barcode.

Okay! Thank you!!