I wanted to clarify that I'm using an SD Card (not the phone internal storage)
I tried both M3U and MPA formats. When I manually copy music to the phone (Windows Explorer copy/paste) everything works. But when I try and sync, all songs are copied to the SC Card (I can see them in the folder view), but Google Play Music refuses to see them, and also doesn't see the Playlists.
This is very frustrating. I'm surprised that I'm the only one who ran into this issue? How do people get music on to their phones?? It's 2014, I'd hate to be manually copying files and manually recreating playlists, considering everything is all nicely organized on my PC in my MusicBee library.