Ya, sorry, .hdanc (non-commercial, Apprentice-created) assets no longer work with the Unreal plugin. They only worked during our experimental/beta stage. You will need to try at least indie assets (so .hdalc) for which you need a Houdini Indie license.

The 30-day trial is for Houdini Engine only, not Houdini.

Alright, at least I know now what the problem is. Thanks!

So if I understand it correctly there is no way to try it out now? I basically need to buy the Houdini to try it out if it works for me?

We do have a 30-day trial for Houdini Engine. It should have kicked in for you the first time you tried to use it in Unreal. If not, you can try to activate it manually. Here are the instructions:
https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=39229 [sidefx.com]