I have a MacBook Pro with El Capitan 10.11.6 signed in to iCloud. I also have an iPhone 6s Plus which is also signed in to iCloud. After upgrading my iPhone to iOS 10 I have follow-ups showing notifications and also frequently appearing push notifications about "approve your device".
I push it, then enter my passcode to iPhone and see this:
Approve This iPhone Go to one of your devices signed in to iCloud to approve this iPhone.
Waiting for approval (spinning wheel)
Sooo... I do not have any popup or window or anything else on my MacBook to approve iPhone. How can I do this?