How to fix iOS 15.8 installation error?

Hi koushik262,

You may want to verify the exact iPhone model (an iPhone 7 can use iOS 15.8), and also provide additional information about the installation problem.

If your iPhone or iPad won't update - Apple Support

Hi pon113,

With an iPhone 6 (not iPhone 6s), the latest version would be iOS 12.5.7. Upgrading to iOS 13 and higher is not possible for hardware reasons.

An iPhone 6s can use iOS 15.8.

iPhone 6

Update iOS 15.8 iPhone 7 Plus