I see an error when I try to redeem a movie on my iOS device.
You can play movies from your UltraViolet collection on iOS devices, but you must redeem them on a desktop or laptop computer. Once you have done so, open the Flixster app (free in the App Store) on your device, then log in on the My Movies tab. You'll see your collection. Tap on a movie poster to view the film's details page, then tap on "Watch Now" to stream, or the purple download button to watch offline.