You have to enable it for managed users in your Plex Home. They cannot enable it themselves. Using Plex Web, go to your Plex Home page, edit the user. The setting is on the Libraries tab.
Note you must edit the managed user to change the setting. You cannot set it when creating the managed user (I did not see it when creating a managed user). It is disabled by default.
At the end of Sync Watch State & Ratings:
Is this available for Managed Users?
An individual managed user cannot alter this setting themselves. However, the admin of the Plex Home can adjust it for a particular managed user from the Plex Home management page.
Users with regular Plex accounts (created w/ an e-mail & password at plex.tv), have to enable it themselves. You cannot enable it for them. It does not matter if they are in your Plex Home or not.
Correct.
The user plex needs at least read-only permission to the media files. If you are creating optimized versions, recording live tv (live tv & dvr), etc. then plex will also need write permission.
In the Linux Tips doc, see the first item, Using Other Hard Drives (Windows or Linux) with PMS., section F. Correct (set) Linux file permissions (ext4 drives only).
