Unable to sync desktop local files to iPhone

[swapnils7]

I'm trying to add some local files to my Spotify to be available for playback on my phone. I followed the procedure specified:
(i) Create a playlist
(ii) Add the tracks to the playlist on the desktop app
(iii) On the iPhone app, go to the new playlist and set Download to 'On' (and wait for the songs to "magically appear").

This doesn't work. I have a premium account, both my devices are on the same network, and the Spotify app is allowed through the firewall on all kinds of networks (I even tried turning firewall off altogether; still didn't work).

Also, I tried reinstalling the apps. Nothing worked.

Help.