On my droid turbo 2 I keep getting an amazon update avail message. But when I go to install it I get a install blocked message. The message says its from an unknown source. I do not understand why its an unknown source as the app is preinstalled on the phone. I do have the switch set to block apps from an unknown source. What's the story, on this. Is the app safe or what? If its not safe, how can I stop the annoying message.