I am developing a iPhone application with integrating Spotify SDK. I am facing some issue regarding premium account and simple account.
I am trying to play song with Spotify simple account without any premium account, but it always showing an error : "The operation failed due to an unspecified issue." and after same song play with premium account they play the song.
Spotify API only supports music playback for users with a Premium Subscription, although the error you're getting could more helpful but this is the reason for the issue you're experiencing.