Indicates whether the channel has been verified or not. It is
illegal to specify this field in a
Sentinel value used to indicate that the
state is unknown, omitted, or is not applicable
(as in the case of channels that neither support
nor require verification in order to function).
The channel has yet to be verified and
requires verification to function. Note that
this state also applies to the case where the
verification process has been initiated by
sending a verification code but where the
verification code has not been submitted to
complete the process.
It has been proven that notifications can be
received on this notification channel and that
someone on the project has access to messages
that are delivered to that channel.