It seems that the upgrade to this version of iOS has been removed for some older devices , as it sometimes got stuck in the part of entering an Apple ID trying to collect the data for that account from the company’s servers.
The affected devices are the iPad 2, 3, 4 and Air; and the iPhone 4S, 5, 5C and 5S . Apple has confirmed the withdrawal of the update to iMore publishers and has promised to restore it within a few days when they find a solution to the problem. A new build is now available for download as an update to iPad 2.
Apple recommends checking that our device is properly activated from the iCloud website and from iTunes
Apple has also published an official support document explaining the error, taking steps to confirm it and try to fix it: you must check from the iCloud website that the device is registered in our name. As a last resort we are also asked to connect the device to a Mac to try to activate it from iTunes.
If you have one of the affected devices and have already successfully updated to iOS 9.3, no problem . This is not unusual, because not everyone is affected by the bug. I myself updated an iPhone 5S and an iPad 3 yesterday and found no obstacles to do so. But if you haven’t updated yet, you’ll have to wait for Apple to restore the update. Remember that this does not affect the iPad Air 2 or iPad Pro or the iPhone 6 or 6s. The iPhone SE and 9.7-inch iPad Pro already have iOS 9.3 installed as standard.