The package name is plexmediaserver-plexpass. The service name is plexmediaserver_plexpass. I don’t know why they did this but, use those values accordingly.
Also I’ve updated the install script, I’ve only tested it in iocage jail, if someone with an older style jail can test it I’d appreciate it. It shouldn’t need to be edited as it finds all of the paths. One thing I’m not sure of is on the older jails, where is your plex installed for each version? Is standard in /usr/local/share/plexmediaserver and the plexpass in /usr/local/share/plexmediaserver-plexpass? If this is true, and the service names are still different, plexmediaserver and also plexmediaserver_plexpass respectively, then my updated script will work.
It pulls auth automatically you don’t need to supply your login/pw creds. It uses the API and your server’s authtoken from the preferences file.
I am not sure if this helps anyone. However I ran into this issue trying to upgrade from 1.12 > 1.14 > 1.16 after FreeNas took a major update. I followed this guy james and just deleted the old Legacy jail and Plugin.