Syncing local files to offline on iPhone

[HPerks18]

I've saved local files to Spotify playlists and synced them offline on my iPhone before. I went to add a few more and now none of them will sync offline. I've tried every solution I've come across so far:

- I've updated spotify on my mac, created a separate playlist for local files, and set every playlist containing local files to offline on mac.

- I've set iTunes to share library xml with other applications

- I've deleted the app then re-installed on my iPhone, sharing the same wifi as my mac i've set playlists containing local files to offline on my iPhone. NONE of the local files have come available on my iPhone (despite being on my iPhone in iTunes)

- Mac and iPhone recognise each other as devices

- Firewall is turned off on Mac

- Signed in with the same account on both devices

Being able to take playlists offline with local files was one of my favourite features of Spotify premium (probably the main reason I've used it for 3 years now), but this sudden problem is really stressing me out. Never had an issue before, really need it fixed. 

Any and all help much appreciated.

Cheers, Peace, & Love