Defines the subscriber audience that will receive this message. You may exclusively provide one of: all_subscribers, segment_ids, external_subscriber_ids, or segment_spec. If providing all_subscribers or segment_ids you may optionally provide excluded_segment_ids. If providing segment_spec you may optionally provide excluded_segment_spec.

Defines when the notification should be sent

Defines the notification details that will be sent

Additional free-form properties for identification and filtering