Server Version#: 1.18.5.2309
Player Version#:8.20.0.26605
Got Plex working on my DSM and can stream through the browser on my PC. Created new shared folders instead of the default and read/write to the Plex user.
When running Plex on my Sony TV or S20+ I am getting:
Movies, TV or home video: An error occurred while attempting to play this video. Please check your connection and try again.
Music: An error occurred while playing this item.
Same errors when Casting to the TV
I can see all the items in the libraries but can not play them. I went through the forums and tried different things but am at a loss right now.
First time Plex user
Edit: There are many reports of problems with the current versions of Andoid/AndroidTV apps and old versions of Plex Media Server (1.18.x, 1.19.x). Updating to a current PMS release resolves the problems for many people.
Update to the current version of Plex Media Server, 1.23.4.4805. Version 1.18.5 was released in January 2020.
You will need to download the current version from plex.tv/download and perform a manual update via the Synology Package Center.