Customers who have upgraded to iOS 10.2 will no longer be able to downgrade their iOS devices to iOS 10.1.1, the previous version of iOS.
Apple routinely stops signing older versions of software updates after new releases come out to encourage customers to stay up to date. iOS 10.2 is the only version of iOS 10 that can be installed on iOS devices, though developers and public beta testers can download iOS 10.2.1, a future update that is currently in a beta testing phase.
Released to the public on December 12, iOS 10.2 introduced major new features like the dedicated TV app, new emoji, and a range of bug fixes. Apple has also stopped signing tvOS 10.0.1 for the fourth-generation Apple TV.