The plugin should soon be available in the 'Download Managers-testing' repo soon.
The plugin should work on most systems (amd64, i386 and arm)
The default username and password for the webui is "openmediavault"
The default download folder is set to /home/nzbget/downloads it is also known as the "MainDir", I suggest you change it to a shared folder location unless you have plenty of room on your system drive.
Please don't ask how to configure NZBGet, this topic is for users who have trouble installing/running the plugin.
REMEMBER it is in the testing repo for a reason