Following the release of iOS 15.4 last week, Apple on Wednesday stopped signing iOS 15.3.1 for all iPhone, iPod touch, and iPad models. This means that users can no longer downgrade their devices to iOS 15.3.1.
iOS 15.4 was released on March 14 with significant new features such as Face ID unlock while wearing a mask, Universal Control for iPads, new emojis, enhancements to iCloud Keychain, and more. The update also adds a new Siri voice for US users and Tap to Pay, which turns the iPhone into a payment terminal for contactless credit and debit cards.
As for iOS 15.3.1, it was released to users on February 10 with a fix for a security exploit found in WebKit, the engine behind Safari. The update also fixed an issue that may cause Braille displays to stop responding.
Reverting to older iOS builds is often used by those who jailbreak their iPhones. Restoring an iPhone or iPad to a previous version of iOS can also sometimes be helpful for users who experience significant bugs after upgrading to the latest version of iOS.
If you have experienced any serious issues with iOS 15.3.1, unfortunately, you’ll now have to wait until a future update rather than downgrading to iOS 15.3. Users running the iOS 15.4 beta can no longer downgrade to iOS 15.3 either.