...

If an item doesn't appear in your preferred Agent's resource, it will not be matched. You can check your preferred Agent resource in the Server Preferences. If the preferred Agent doesn't match the item, you can try a different Agent using the Fix Incorrect Match tool.

Using Plex with a NAS to Store Your Media

... to put instructions here ... 

References

https://plexapp.zendesk.com/hc/en-us/articles/200288586-Installation
install avahi-utils first

...