WebhookDelivery

attempted_at
Type: stringFormat: date-time
required

When this attempt ended (your endpoint answered or the call failed), in UTC. The t in Roster-Signature is when the delivery was signed and sent, slightly earlier.
event_id
Type: string
required

Unique identifier of this notice. If it arrives again with the same identifier, do not count it as a new change.
event_type
Type: string
required

An event type, or webhook.test for test deliveries.
outcome
Type: "delivered" or "failed"enum
required

Delivered means the receiver acknowledged this attempt; failed means it did not. A later retry has its own attempt record.
status_code
Type: integer | null
required

HTTP status your endpoint returned, or null when there is none to report — the endpoint was unreachable, did not answer in time, or answered with a redirect, which Roster refuses without following.