Wow! I got it. Just went down the line in TureNAS settings trying everything. Suddenly there it was a “Claim this server” link which I followed and it worked. Cant say how it happened exactly I was all over the place but after 2 days Plex server is back!
If you installed this via plugin I wonder what server version you are on. The plugin has not been updated in a very long time, and you would need to use a separate solution to update further.
