I don't see any availability for this train, just the grey "!” that normally means there are no more pass holder seats available. The number of pass holder seats in these international TGVs is limited and since it's a Sunday evening, it's quite possible that there are none left. They're also quite expensive at 35€. You could ask at a Swiss ticket office just to be sure; they can also book this train. But the Interrail website does show availability in the same TGV 1 day later so there's no general booking problem and it's probable there just no more pass holder seats.

Alternatives are to use a TGV until Strasbourg or Mulhouse (10 or 20€ depending on availability), TER to Basel and IC to Zurich.

Assuming you're booked on the Thalys that arrives in Paris Nord at 16:44, this would be possible:

TGV 9591 still has 10€ seats available (also available at a Swiss ticket office). Paris Est is just a 10 minute walk from Paris Nord.

Normally I'd advise to travel via Germany (optional reservation for just 4€) but on this day, there are engineering works between Offenburg and Freiburg(Breisgau), so you either need to take a bus there or travel via Stuttgart.

hi thanks for the response! however, i tried to book the 4:21pm train from Paris gare de lyon which has high availability but im still facing the error at the checkout page. 

I can get to the payment page for the train from Paris on 10 April at 4:21 PM. Are you seeing the same error message as in your original description? If not, then which one?

If you really want that train, maybe it's better to go to a Swiss ticket office.

By the way, the price in USD seems to be about 3.6% above the middle rate, which is a bit expensive IMO. Unless your credit card provider/bank charges more than that, it's better to pay in euro. In general, it's cheaper to choose to pay in the local currency.