So, it appears that RailEurope has started to charge "reservation fees" for SNCF reservations. A week or so ago I made this same booking on this same site and was not charged an extra fee.
This means that unless you actually go to a physical SNCF ticket office, phone SNCF, or buy it with a ticket, there is currently no way to buy a compulsory seat reservation without paying an extra fee on top of the cost of the reservation itself. Which instantly makes the already outrageous fees 2€ pricier for everybody.
It also means that despite SNCF reservations being fully refundable, you will still lose your 2€ reservation fee if you need to cancel.
@moof This reminds me I need to book some reservations for tomorrow, but #HappyRail can't show me seats for tomorrow's trains. Pot luck horror. Or should I got l go to the station?