Apple TV device verification
Where do I enter the 6 digit verification code on my Apple TV device?
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What model of Apple TV do you have exactly?
For 4th generation and later, it should offer a set of boxes to enter the code in on screen.
For 3rd generation Apple TV and earlier, you would need to enter it along with the Apple ID password in the entry box for the password. Together with no spaces.
See here for details: link-> Two-factor authentication for Apple ID on older devices - Apple Support