curl -X PUT "https://api.unipay.com/v1/webhooks/wh_123" \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"events": ["transaction.completed", "transaction.failed"]}'

{
  "webhookId": "wh_123",
  "url": "https://your-app.com/webhooks",
  "events": ["transaction.completed", "transaction.failed"],
  "updatedAt": "2026-04-22T12:30:00Z"
}