Somebody else posted this:
- From an iPhone or iPad, go into "Settings" => click on the top bar with your name and "Apple ID, iCloud, iTunes & App Store".
- While still on iPhone or iPad, tap on "Password & Security", then tap on "Get Verification Code", LEAVE the supplied verification code visible.
- Go to the iTunes login on your AppleTV settings and start logging in.
- When it asks for your password, enter your password and add the verification code to the end of your password BUT DO NOT HIT SUBMIT YET !!!
- Go back to your iPhone/iPad and tap on "OK" on the verification code to make it go away.
- Now go back to your AppleTV and submit the password.