The error code of PlayStream subscription result.
        private static void OnSubscriptionErrorCallback(object[] data)
        {
            var message = data[0] as string;

            if (OnFailed != null)
            {
                if (message == "Invalid Title Secret Key!")
                {
                    OnFailed(SubscriptionError.InvalidSecretKey);
                }
                else
                {
                    OnFailed(SubscriptionError.FailWithUnexpected(message));
                }
            }
        }