One song won't sync to my iPhone from Apple Music on Mac

There is one song in my Apple Music library, on my computer, that came from an mp3 file I have saved on my computer. It will not sync to my phone - on my Apple Music app it appears but is grayed out and won't play. When I click on it says that I have to go onto my Mac and select "sync library."

However - "sync library" is checked. On both my Macbook and my iPhone. On my iPhone I turned it off and on again. It still does not let me play this song.

I don't want to turn off, then on, "sync library" on my Macbook, because I'm afraid it'll delete EVERYTHING, including other songs I have downloaded from Bandcamp etc. and not right through my Apple Music account.

I just want to play this song on my phone :( Help!