I can't install the current version 3.0.0 of the Spotify iOS app on my iPod Touch 4th gen since that model is limited to iOS 6, but I was able to get the older version 184.108.40.206 of the Spotify app to install by adding Spotify in iTunes and then requesting the latest compatible version on the device. (Spotify Premium)
The app works, but the sound suddenly cuts off after a random interval of a few minutes. The music still appears to be streaming in the Spotify app, but nothing will restore the sound output from the iPod. I can go to another music app and play sound just fine. But there's still no sound from Spotify when I switch back to the Spotify app. The only thing I can do is terminate the Spotify app and restart it to get the sound back. Pausing and resuming doesn't work, nor does selecting a new tune. Same on Bluetooth output. I've tried switching between Normal and High quality - no effect on the problem.