Netclient Error while connecting to Netmaker Server (Debian 11)

[stefan4427]

The Netclient on a Debian 11 System is not connecting properly to the Netmaker Server.
The Netmaker Dashboard shows the Client connected, but health status is "Error". Problem is the Dashboard telling nothing about the exact problem. The error handling and troubleshooting is quit poor.
There are no error messages at all, despite of one error in the journal saying "host setting server config is nil" (it really says nil).
I have no clue how I shall troubleshoot this problem, how am I supposed to solve this?
I did already basic troubleshooting to the point where I completely reinstalled the whole server. Please help me, thanks.