I have two music libraries in my Plex Server. With the Plexamp desktop app I’m able to select the source but if I’m using my Amazon Echo Dot and I try to use Library Radio or Time Travel Radio, Alexa Skill defaults to my first music library which is not the one I want to use.
How can I change the default music library source for Alexa?
(I’ve asked the voice control team to reply.)
Actually, see https://forums.plex.tv/discussion/317907/another-library-radio-question#latest for an answer 
Thanks elan. That helps.
Unfortunately, this link is no longer working so the answer I was eager to read can no longer be viewed. 
Weird, try this: Another Library Radio question
