one song doesn't sync on iphone

[IlianKai]

on a premium (family) account : 

1/ placed an mp3 file in a music folder on imac

2/ configured spotify to sync with this folder (via spotify player on imac)

 -> observation: song appears in local files

3/ added music to playlist

  -> observation : no icon appears to add/remove song to 'your music'

  -> observation : can play son on imac

4/ playlist was already synced with iphone (also for offline)

 -> context: phone is on the same wifi network as imac

 -> observation : on iphone song remains grayed out in the playlist

 -> observation : all other songs in that playlist are active and downloaded

 -> observation : at the top of the playlist, the 'download' button is active and shows 'waiting for download'

what do we need to do make this song playable on the iphone ?  

-> none of the posts i found provided any help.  

[IlianKai · Accepted solution]

we tried adding the file a second time.

the app replied with 'do you want to add a duplicate'.  after saying 'yes', the song got added, suddenly making both copies available on the iphone...

Even after deleting one copy, the song remained playable on the iphone.  

so 'solved' I guess..   hope anyone else experiencing this 'glitch' is helped by our post 🙂