{"status":"ok","message":"Webhook endpoint is ready to receive listings","endpoint":"/api/webhook/listings","method":"POST","authentication":"required (x-api-key header)","idempotency":"supported (x-idempotency-key header)","documentation":{"headers":{"Content-Type":"application/json","x-api-key":"your-webhook-secret (if configured)","x-idempotency-key":"unique-request-id (optional)"}}}