Create webhook

Message events POST one payload shape regardless of where in the pipeline the state change happened: { "id", "to", "channel", "status", "error_code", "error_message" } — the two error fields are present only on failed/undeliverable events and carry the same values as the stored message (see the Message schema). id is the EnvoiSMS message id, the same one the send call returned. metadata supplied at send time is included on delivery-report events.