For Thalys trains, it's possible to reserve here, too:

https://www.b-europe.com/EN/Booking/Pass#TravelWish

You can't see availability until you're logged in or click on the train. This route is very popular so it's likely that your train has sold out (Thalys also have passholder quotas...).

Alternatives :

- another available Thalys for 27€ (07:13, 15:37, 17:16, 20:13)

Option 2 :

- IC Brussels - Tournai - Lille-Flandres

- TGV Lille-Flandres - Paris-Nord 10€ limited fare (but pretty much always available), then 20€

Option 3 (fully free but infrequent connection) :

- IC Brussels - Charleroi-Central

- R Charleroi-Central - Maubeuge

- TER Maubeuge - Paris-Nord

Cool thanks...