Playing downloaded music from Play Music app

[Ben_70]

I have songs downloaded to the Play Music app that I would like to cast to my Google Home. The casting action seems to go fine (the Home beeps and my phone recognizes my named Home speaker) but if I try to play a song (any song) I get a pop up in Play Music, "Can't play this song. To play the song, upload it to Play Music from your computer."
What the heck is that supposed to mean?!? The songs have been uploaded to Play Music from my computer. That's how they got on my phone.
Note, I do not subscribe to Play Music. Also I can get Home to play music but they're not the songs downloaded on my phone.