I'm trying to display an iFrame with a song and when I try to play the song I get the message "This track is not available in your country". I can definitely play the track from my local Spotify. Also, I'm in the US so that shouldn't really be a problem for most tracks. I noticed that I was able to play all of the tracks after I signed in to this forum.
Does the iFrame look for a cookie and thus works differently for authenticated users vs not? My impression was that the iFrame was a tool to allow users to preview a track with our without a Spotify account.