Apple ID Verification - Endless Loop - Solution Here

Background:

- I have 2 iPhones: (1) iPhone 4 with iOS 7x, and (2) iPhone 7 with iOS11x)

- Two-factor authentication already turned on for years, using my iPhone 4 as the primary phone for authentication

- Just set up new iPhone 7 with same Apple ID as the one used on iPhone 4

Problem:

- iPhone 4 started asking for Apple ID authentication, but authentication process never completes after clicking on all the right things, and authentication requests keeps on popping up on screen.

- I assume this problem only happens if you have an old apple device that could not be upgraded to iOS 9 or later.

Problem Started After:

- I set up my new iPhone 7; and

- I was asked to authenticate for something (sorry forgot what it was) and I saw the prompt on my iPhone 7 to authenticate. I clicked on iPhone 7 to authenticate.

Should have:

- I should have used my iPhone 4 to authenticate (not the iPhone 7).

SOLUTION to resolve endless Apple ID authentication requests:

- Log off from iCloud on all apple devices. "Delete" iCloud account from iPhone 4.

- Restart all apple devices.

- Log on to https://appleid.apple.com/

- Disable Two-Factor Authentication

- Log on to iCloud on apple devices with Apple ID.

- Log on to https://appleid.apple.com/

- Enable Two-Step Authentication via https://appleid.apple.com/manage/security/2sv/enrollment

( Do not enable Two-Factor Authentication - different to Two-Step Authentication)