Create a webhook subscription (one-time reveal of the signing secret)

Subscribe an https endpoint to filing.ingested (a filing whose values are served, filed within the last 45 days) and restatement.material (that filing restates an earlier value beyond the materiality wall: medium or high). Optionally scoped to a list of entities; otherwise every entity your workspace can see. Enterprise plan (scope webhooks.manage): 401 anonymous, 403 otherwise. At most 10 active subscriptions per workspace (409). Every delivery is a POST from 178.104.6.216 of a compact JSON body with sorted keys ({"id", "event", "created_at", "data"}) and four headers: X-Hub-Equity-Event, X-Hub-Equity-Delivery (uuid), X-Hub-Equity-Timestamp (unix seconds) and X-Hub-Equity-Signature: v1=<hex> where hex is HMAC-SHA256(secret, <timestamp>.<raw body>); for 24 hours after a secret rotation the header carries two signatures, v1=<new>,v1=<old>, and any match verifies. Verify on the raw bytes with a constant-time comparison and reject a timestamp more than 5 minutes from your clock. Delivery is at-least-once and unordered: deduplicate on X-Hub-Equity-Delivery. Answer 2xx within 10 seconds; anything else is retried after 1 min, 5 min, 30 min, 6 h and 24 h, except a 4xx (other than 408 and 429), which is final. Twenty consecutive failed attempts pause the subscription; resume it with PATCH {"is_active": true}. Events cover filings ingested after the subscription with a filing date under 45 days; to catch up after an outage, read GET /entities/changes?since=.

filing.ingested data: {entity_id, entity_name, filing_id, form_type, fiscal_year, period_end, filing_date, ingested_at, viewer_url}. restatement.material data: the same plus restatements: [{hub_concept_code, hub_label, fiscal_year, original_value, restated_value, delta_pct, materiality}] (materiality medium or high).