# 13806: Invalid Client Notification URL

Log Type: APPLICATION

Log Level: ERROR

## Description

This error means the configured `clientNotificationUrl` is not a valid URL for Voice client call notifications. Twilio uses `clientNotificationUrl` to notify your application when a call routes to a Voice SDK client user, and the URL must contain a valid hostname, cannot include underscores, and only accepts `POST`.

### Possible causes

* The configured `clientNotificationUrl` is malformed or otherwise not a valid URL.
* The URL hostname is invalid or includes underscores.
* The URL is not configured to use `POST`.

### Possible solutions

* Replace `clientNotificationUrl` with a valid URL that uses a valid hostname and does not include underscores.
* Configure the notification endpoint to accept `POST` requests.
* Verify your webhook handler responds appropriately to client call notifications. Twilio sends the request body as JSON, and the endpoint should return `200 OK` when a matching client binding is found or `404 Not Found` when it is not.

#### Additional resources

* [TwiML Voice: `<Client>`](/docs/voice/twiml/client)
* [Client Call Notification Webhook](/docs/voice/sdks/client-call-notification-webhook)