Signing for iOS 18.6.2 has been stopped by Apple. If you have updated your iPhone to iOS 26 you are no longer allowed to downgrade back to iOS 18. iOS 26 was released by Apple one week ago. When Apple signs software, it means the new version passed a verification check on the server side.
This verification check is done by Apple whenever new software is installed for the iPhone, which aims to keep the device secure. The software cannot be installed until it passes Apple’s verification check. Apple unsigns previous updates to stop its users from downgrading, or new users from installing an outdated version of iOS that is less secure after the upgraded software becomes available.
tvOS 18.6 and iPadOS 18.6.2 are no longer signed by Apple, so there is no option to go back to the previous version. This is done to keep users safe and protect them from potential risks on their iPhones.
