From the NS International website...
Destinations purchasable at ticket machines
Also you could use the
NS Mobile App...
It is possible to book a mobile ticket for Thalys to Antwerp, Brussels, Lille and Paris and for all destinations in Belgium and Germany. A mobile ticket is a ticket for a smartphone. The ticket includes a square barcode, that has registered your travel information. This barcode can be scanned on your phone when on board the train.