You did not say for which day. It is very rare, but not impossible for trains at populair times to get fully booked-though often this is only for some segment in the total trip. In FR of course most often to/fro Paris=final leg. There ARE much slower local=TER trains, always unreserved, via the old classic lines, that can bring you Strsb-Par, but it may mean you may have to change total plan. Or do the same from Bael-or even via the new line Delémont-Belfort, then on to Paris.

TGV inside FR have QUOTA for Passholders-if you are lucky to get in, it will cost you 10€, otherwise its 20. What it means in your case is hard to say.

Try if a SBB counter can help you out if you are now in CH anyway.

The Interrail reservation service still does not show the 20 EUR reservations when the 10 EUR ones are sold out. You can also check availability via Belgian railways. To book via that website, you need a pass cover number and it’s 4 EUR extra per order (instead of Interrail’s own fee of 2 EUR per person and train), so trying a Swiss ticket office sounds like a good idea.

Thanks a lot for your reply. It’s just unbelievably complicated trying to do Eurail on CH-Paris-London, particularly when TGV & Eurostar are involved, with all the restrictions, supplements, reservations etc, a real nightmare.  SBB didn’t tell me that. However, they made up for it by arranging the Suisse-Paris legs (they’re still unable to book beyond Paris, a Covid legacy apparently. Not easy avoiding flights, but heigh ho. Cheers, Grizz

Thanks. You are right. Without the Swiss customer service it would have been a no-hoper.

However, one of their people did suggest Global Pass in the 1st place so either they felt somehow responsible, or the lady felt pity