How to turn off two-factor authentication on my iPhone?
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How to turn off two step verification
[Re-Titled by Moderator]
iPhone 4s
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if enabled when the Apple ID was created, or if enabled for more than two weeks, two-factor authentication cannot be disabled. Within the two weeks, use the link in the mail message that was received when two-factor was enabled.
if you really meant the older two-step verification, see this: Two-step verification for Apple ID - Apple Support
If you're not sure if you’re using the older (iOS 8 or macOS 10.10 or earlier) two-step verification or the less-old (iOS 9 and macOS 10.11 and later) two-factor authentication, see the section “Confirm which feature you're using“ in the link above.