Order-side v2 payloads use api_version: "2026-08-17". Deduplicate on event_id. Live envelopes also include timestamp_epoch (integer Unix seconds next to ISO timestamp).
The ORDER allowlist includes first_purchase, plan_type, and attribution. first_purchase and plan_type are included only when an ecommerce order is resolved. attribution is included only when tracking data was captured. See Webhooks v2 — Overview and Attribution Passthrough.