### Typical Request-Response Cycle

1. An event (e.g., call.answered) occurs in the Voice API.
2. The API sends a POST request to the configured webhook endpoint with event details.
3. The server processes the event and responds with SVAML commands (e.g., play a message, gather input).
4. The API executes the commands and updates the call state.


```mermaid
sequenceDiagram
  participant VoiceAPI as Voice API
  participant Backend as Application Backend
  VoiceAPI ->> Backend: POST webhook (event details)
  Backend ->> VoiceAPI: SVAML commands (response)
  VoiceAPI ->> Backend: Further webhooks (if needed)
  Backend ->> VoiceAPI: Additional SVAML commands
```

Webhook endpoints must respond within 5 seconds. If the endpoint fails or times out and a `fallbackUrl` is configured, the request is re-sent to the fallback URL. See *Timeouts and failover* in the **Webhooks** section for the algorithm and its effect on delivery guarantees.