Apple ID verification

Try using What to do after you change your Apple ID or password https://support.apple.com/en-us/HT204071

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If the above step does not help, note I have not seen a definitive solution for your problem. So, I suggest you use my search link in trying to solve it: verification failed unknown error apple. You will see a number of links that are, or may be, related to your specific problem. Several links related to my search claim fixes.

If you want to contact Apple Support to deal with your problem, see:

Get a call from Apple support to help solve your problem using this link https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362 Be patient. Sometime this site is not fully functional.

Apple ID Support https://support.apple.com/apple-id

Apple Support Twitter https://twitter.com/AppleSupport  There may be a wait of an hour or so.

Apple ID account security for country-specific and region-specific help https://support.apple.com/en-us/HT204169

Get Support: We’re here to help https://getsupport.apple.com/. Go through the options to find the best one.

Device or computer? Are you running any anti - virus programs? Using a VPN?

 Do you have access to another WiFi network where you can try? That has worked for several people.

You are welcome.