I have an mp3 song that I'd like to play on my Spotify app (premium account) on my Android phone. The song is not available from Spotify itself. It plays fine in my desktop Spotify app (Windows 10), but it's greyed out and won't play on my phone, despite the fact that the "downloaded" switch for the playlist is turned on both on my desktop app and on my phone app. Both devices are on the same wi-fi network.
I've seen a bunch of similar threads but nothing has helped me. I've tried logging out of the app and logging back in. Yes, I've tried turning it off and turning it back on again. The mp3 in question is also on my phone's SD card and plays fine in another music player.
I have other local files that aren't available from Spotify that play fine, but this song (and a few others) won't play. Any ideas?