Premium Music

I have a PLEX Pass account and I’m trying to follow the on line guide to build a Premium Music set up on my Nvidia Shield. When adding a music library, I’m not seeing the option to create a Premium Music Library icon as indicated on the PLEX guide on how to set up said library. I’m accessing my PMS on the Nvidia Shield from an Ubuntu desktop and tried it on a Windows 10 laptop, and neither platform gives me this option. I’m signed in with my PLEX Pass account and I’m signed in on the PMS. What steps am I missing?