That is strange, since your journey only goes via the Netherlands and Belgium. Could you please verify your country of residence under My Pass > +Details?

I am really sorry, I clicked the solved button and there is no undo. I still struggle with the same issue

That explains it. You bought a pass with residence "Netherlands”. If that is not correct (your profile says Austria), then contact customer service ASAP to correct this and mention you're currently travelling.

If the Netherlands is your country of residence, then the warning is correct.

Customer Service is not replying quick enough, and the chat bots are a joke.

I don't understand what my residence has to do with the trip or the pass? My residence is indeed im the Netherlands… only my passport is still from Austria 

Residence is all that counts. Your pass is therefore not valid in the Netherlands.

Thank you for the information. How can I change my residence?

Via customer service.

The right answer is: moving home.

There is indeed a rule that you have overlooked: you cannot freely ´choose´ where you live. And there is indeed a restriction on travelling in home-country since InterRail started-as is of course explicitly stated in rules. In the past-when passes were sold at station-this was then of course checked/warned at. This mainly restricts f.e. people from DE or UK-big countries where trainfares are quite high- to ´choose´ another country and then travel a lot in their own for much less as the railways would like to.

BTW; LUX is free and in BE there are very cheap GO_pass junior fares (about 7 €/trip)