SOLVED "unable to play media" error Galaxy S7 connected to home Plex Server

Not sure what is going on. S7 connects and sees available “Watch Later” media, but gives “unable to play media” error.
Media plays fine on a remote PC connection (Win 10) to Plex Server.

Update: Just discovered that if I switch to a lower resolution, the videos play just fine on the S7. I must have tweaked a setting on my Plex Server that limited videos to 720.