{
  "_comment": "ActiveCampaign → Settings → Developer → Webhooks → Add, or the body of POST https://<account>.api-us1.com/api/3/webhooks. URL: your relay's HTTPS URL (port 443) followed by /<RELAY_SECRET>. Only the subscribe event (Contact added) is needed; the relay ignores the others. To check only one list's new contacts, add \"listid\": <the list id> to the webhook object.",
  "webhook": {
    "name": "email-validation.org: check new contacts",
    "url": "https://<your-relay-host>/<the same long random string as the relay's RELAY_SECRET>",
    "events": ["subscribe"],
    "sources": ["public", "admin", "api", "system"]
  }
}