I have this same problem, I cant connect Sonarr to plex anymore.
https://www.reddit.com/r/PleX/comments/542kui/plexcheck_updated_for_plexs_recent_token/
It seems like the PLEX api requires a token now, but the thing is… Im not using a plex account. Im not signed in on Plex Media server.
So how am I supposed to get a token?
When I follow those steps, there are no token in the URL.