The verification code that was delivered to the channel as a
result of invoking the
SendNotificationChannelVerificationCode API method or that
was retrieved from a verified channel via
GetNotificationChannelVerificationCode. For example, one
might have "G-123456" or "TKNZGhhd2EyN3I1MnRnMjRv" (in
general, one is only guaranteed that the code is valid UTF-8;
one should not make any assumptions regarding the structure or
format of the code).