Sends a request for each registered event type to the registered URL.

The payload will be generated from the last entity that would have invoked the web hook. If no entity is present for none of the registered event types, the POST will respond with 204. If a test request can be made, it will respond with 200. The request will contain a X-MicrosoftSpeechServices-Event header with the respective registered event type. If the web hook was registered with a secret it will contain a X-MicrosoftSpeechServices-Signature header with an SHA256 hash of the payload with the secret as HMAC key. The hash is base64 encoded.