Sharing with Spotify users that are not on Facebook won't work on iPhone App

[user-removed]

Why I can find and share tracks with Spotify users that are not in Facebook, on my Mac but not with my iPhone App? I used to be able to do this, until a few updates ago. 

I have almost 1000 tracks in my inbox that a Spotify user friend of mine has shared with me. While I receive music from all my friends (Facebook or on Spotify), I can not share back with them, since Spotify App does not find or recognize them. I am following the user and everything is working Ok but I can not find, share or review a Spotify user on my iPhone App, even when I am following, or have received thousands of tracks from them.

What am I missing?

Best

Parsa