The last payment window is no longer in progress.

I'd like to reserve a seat for the train from Barcelona to Paris on December 16. I'm trying to pay 10 euros because it's marked as mail delivery, but the payment is no longer processed because it's being replaced with an electronic ticket. 

I can't even book a seat on the train from Paris to London on December 21. This section is displayed as an electronic ticket from the beginning, but no further progress is made in the last payment window. 

What should I do? You try many times and try for several days, but you still fail. I look forward to your help.