Local Files Don't Show Up On Mobile

[puncho]

Details: premium plan on iOS 10 on an iPhone Xs/macOS sierra

I understand how to port local files onto my phone from my computer, as i have successfully done it before, but now that I'm trying to do it again, the playlists I create to house the local files show up as empty, no matter what I try. Is there some sort of requirements list for a song to be playable on the phone? I can edit the artist, album art, name, album name, etc. on the computer, and the songs that work have different properties than the ones that dont, so this might have something to do with it.

[Emilia_8]

Here's an article on how to access local files on mobile: https://support.spotify.com/us/using_spotify/features/listen-to-local-files/