If you've got it working then obviously it must be possible, but I'm a touch confused because the ErsatzTV documentation says "A Plex Pass is required for ErsatzTV to work with Plex." (https://ersatztv.org/docs/user-guide/configure-clients)

Is it possible that you had this working in the past but Plex has since removed the functionality from their free tier?

I've never had a Plex Pass and I currently use ErsatzTV through Plex daily. I also tried out Tunarr this afternoon and got it working. Though I'll be sticking with ErsatzTV.

Ah, I thought that connecting a custom Live TV source to Plex required the pass. If that is not the case, I can remove the line from the README!