The discount fare mentioned won't necessarily be available every day or for all trains. However a quick search did find one-way, non-stop fares for Sep 28 on Thalys (
https://www.thalys.com/nl/en/).
Bruxelles-Midi (Be) - Amsterdam Central (NL)
Dep 11:52, Arr 13:42 € 55,00 Second class, € 49,00 First Class :-:
Dep 13:52, Arr 15:42 € 45,00 Second Class, € 65,00 First Class
Happy travels!