I downloaded living scriptures and pure flix for our Roku cant get them to play.
I don’t understand the relevance of your post to Plex and Plex Media Server
Pure Flix is a streaming service like Netflix ? How does Plex and Plex Media Server come into it
Pure Flix - is a Roku Channel (App) - doesn’t have anything to do with Plex.
You install the Channel (App) on your Roku and play stuff from there.
Same deal with Living Scriptures:
These two Channels (Apps) are outside purview of Plex.
Plex is for playing personal media (Movies, TV Shows, Music, etc.) that you acquire - one way or another - and store locally on your local storage devices (Hard Drives and such). Plex is the Server/Client relationship that will get those locally stored files from your Server to your Roku.