Can't request questions of a specific level when retrieving api-call data

I’m using the german branch opentrivia.de, have successfully requested the category listing and a few sample questions .. but when retrieving questions I want to use the described api-call.

But as soon as I submit category_id and level - I always get a response code 2 which means incorrect parameter .. but its exactle the line from the website ?? Any clues or is there a more suitable place to ask about opentrivia.de ?

Thanks

Sorry, we don’t manage opentrivia.de. They seem to have a contact page here: Open Trivia DE

Unfortunately their mailserver seems incorrectly configured .. cant send them a short email.