Plex app for Panasonic Smart Viera

Just wanted to thank @ClosestStorm and @shippi for their help.
I managed to install Plex on my Panny TX58DX700B
I’m new with this so had to do some research on how to side load the app.
For those like me I found enough info HERE on how to enable the DevTool on the Panny and side load an app via WebIDE

I can sign in and link the TV to my account, but it then stays on the activating screen. If I switch off the TV and restart it, I then launch Plex and I eventually end up with this error message: NS_ERROR_ILLEGAL_VALUE:

Any idea?