# 5. Start server (optional)
app.run()
```  
1. We define a custom UI using Gradio blocks. This UI will be displayed on the landing page of the server.
2. We create a [`WebhooksServer`] object with a custom UI and a secret. The secret is optional and can be set with
the `WEBHOOK_SECRET` environment variable.
3. We register a webhook with an explicit name. This will create an endpoint at `/webhooks/say_hello`.