Prepares to subscribe an endpoint by sending the endpoint a confirmation message. To actually create a subscription, the endpoint owner must call the ConfirmSubscription
action with the token from the confirmation message. Confirmation tokens are valid for three days.
/// Indicates that the user has been denied access to the requested resource.
///
/// Indicates an internal service error.
///
/// Indicates that a request parameter does not comply with the associated constraints.
///
/// Indicates that the requested resource does not exist.
///
/// Indicates that the customer already owns the maximum allowed number of subscriptions.
///