Plugins

Plex is an available plugin (Lots of resource on how to install).  The FreeNAS team have posted an awesome youtube video.

Jail

The Jail setting is new to me. I’m not that well versed in FreeBSD. Virtually no writes to the USB are allowed; naturally it makes sense that you need to create storage volumes for services.

After installing plex you will need to update it

'jls'  - take the note of the #
'jexec # csh' (where # is the number of the jail)
'fetch -o PMS_Updater.sh https://raw.githubusercontent.com/mstinaff/PMS_Updater/master/PMS_Updater.sh'
'chmod 755 PMS_Updater.sh'

Then execute the script:
Public  './PMS_Updater.sh' 
or 
Subscription './PMS_Updater.sh -u PlexPass_User -p PlexPass_password'