Bonjour Whuechuke62
For the train you indicated 1st class seats are certainly sold out. Two solutions:
– You travel without reservations and find other free seats. Usually you have two 1st class carriages (#1 and #7) and a third one without number in the peak periods.
– You choose another train earlier or later. Be sure that you have a regular Point-to-point Class Upgrade and not a Supersaver Class Upgrade.