iPhone Unavailable. Try again in 8 hours.

This happens after too many failed login attempts. It's an anti-theft technique used to deter thieves (phones are less attractive targets if they're not able to resell them as usable items).

If this is your phone and you know the correct passcode, you can follow the steps at If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support to unlock it.

If this is a new-to-you phone that you bought used, and the seller didn't unlock it or give you the passcode, you may have been scammed.

Either wait the 8 hours or -

If you forgot the passcode on your iPhone, or your iPhone is disabled or unavailable -

Click on the link for instructions on how to reset your passcode without a computer if you have iOS 15.2 or higher.

If you see a iPhone, iPad, or Apple Vision Pro unavailable message or Security Lockout screen - Apple Support

Click on the link for instructions on how to reset your passcode using a computer.

If you forgot your iPhone passcode or your iPhone is disabled - Apple Support