[All Platforms][Playlists] Cannot sync computer files to iPhone playlists

[texafsc11]

I've been trying to solve this problem and I've tried everything and I can't fix it. Here's my issue: I have playlists made that involve both songs I have been able to find on Spotify, and songs that aren't on Spotify but that are from my computer (iTunes). The songs from my computer can be played if I'm on spotify on my Mac, but on my iPhone the songs are just gray/black and can't be played. When I click them it says, "song not downloaded". I've tried to sync the songs by having both devices on the same wifi, making the playlists available offline on both devices, creating a separate playlist on my Mac of all the local files, everything I have seen suggested how to fix the problem and nothing works. Also, the "local files" tab on my iPhone is blank even though there thousands of songs in it on my Mac. The playlists that have mixed music from my computer and Spotify just keep saying, "waiting to download" on my phone. Another thing I saw said to do something about clicking "devices" on the Spotify on my Mac, but that's not even a tab? I really don't know what to do here and I've had this problem since I first got Spotify last year. Please help. 

[MikeATL]

Same problem here. And I have a pretty decent amount of music that's not in Spotify's library. This works without a hitch on Google Music, and seriously has me considering switching.