I allready changed the cluser-name and the node-names to names without _ or -
But it changed nothing on the behavoir.
I opened a ticket at NetApp Support and they told me I should try the ZExplorer Tool, which is also a part of the SDK, and test if I can connect to the API. And yes, it's working. With ZExplorer I can connect to API and execute "system-get-version" for example. I also got some commands from Support to restart the Webserver which is responsible for the API on my FAS8020, but it doesn't helped.
So, now I'm here, becuase the offical Answer from NetApp is"
For now the Netapp Manageability SDK and custom scripts are supported only in the community and not by Netapp Technical support" .... YAY..... But at least the technican I spooke with is trying to reproduce this in his lab. But this takes "some" time.