I cannot sync songs unless I play them on the device. For instance, if I want song A to be available offline on my Ipad, then I have to play the entire song on the Ipad--same thing with the Iphone. Bad thing is that if I play it in either, it's not available offline in both, but only in the device where it was played.
Also spotify doesn't recognize my iphone when I want to sync. Both my laptop and my phone are connected to the same Wifi and I have opened the Spotify app.