If both Plex and Plexamp aren’t working, likely a network issue. You haven’t specified how you’re accessing Plex via the web app, whether directly e.g. http://10.0.0.99:32400/ or via plex.tv.
Regardless, it’s hard to help without more concrete details like Plexamp logs. Make sure your server is signed in and remote access is enabled and green, that’s where I would start.
