Tip!: The Mobile Sync feature requires an active Plex Pass - for the Ultimate Plex Experience subscription for the main Plex Media Server account.
It is possible to enable Mobile Sync for shared users if your Plex Media Server is signed in using a Plex account with an active Plex Pass subscription.
Enabling Mobile Sync for Shared Users
When you create or edit a Server Share, you can choose to allow syncing for the shared user.
Using Mobile Sync as a Shared User
If another Plex user has shared with you and enabled syncing for your share, then you can sync items as normal on the mobile device.
Note: Plex Web App does not yet support shared syncing and will not allow you to monitor or edit syncs against a shared Server. Instead, use the device to which you’re syncing.
Related Page: Sync Media to a Device