Often there are 2 Thalys trains that run together, but have two train numbers.

Thalys 9422 runs from Amsterdam to Paris via Brussel. In Brussel the train from Amsterdam will get together with the Thalys 9322 Brussel-Paris. 

Thank you for the reply - so will this be a problem if my journey is 9322 in my app, but my seat reservation is for 9422?

I can’t get 9422 to come up in the app to add it to my journey.

Try checking for the train leaving Amsterdam and add that to your pass. Even though the reservation is from Brussels your pass will show it from Amsterdam to Paris so no problem.

Alternatively you can add it manually with the 9422 number.

It won't be a problem whatsoever, Thalys staff is well aware these trains run together and won't mind the wrong train number in the pass. The train number is actually optional information when filling in a manual entry. Do board the train listed on your reservation though, as that's where your reserved seat will be.

Fortunately, the coach numbers will be different in both train sets, so that should work without knowing the train number...