Ipad no longer works

See If you see an error when you update or restore your iPhone, iPad, or iPod https://support.apple.com/en-us/HT201210

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And note that receiving the message you received is common. But, I have not seen a definitive solution for it. I suggest you use my search link in trying to solve your problem:  verification failed unknown error apple. You will see a number of links that are, or may be, related to your specific problem. 

And, 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

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

Apple Support Twitter https://twitter.com/AppleSupport

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.

If you are using IOS 8 as your profile shows, how are you entering the code? If you see a password box, enter the password (ABC) followed by the code (123) or ABC123 (no spaces).