When you create an Event Grid subscription pointing at a custom webhook, what must the endpoint do before events flow?

1. A Return HTTP 200 to any request
2. ✓ B Complete the subscription validation handshake by echoing the validationCode or calling the validationUrl (correct answer)
3. C Present a client certificate
4. D Register a SAS token

Shortcut: Event Grid posts a SubscriptionValidationEvent. The endpoint must echo validationCode synchronously, or fetch validationUrl asynchronously, proving ownership before deliveries begin.