You attempted to initiate an outbound phone call, but the URL you specified to handle the call was not a valid URL.
If you specified an Application Sid for your outbound phone call, the application must have a valid VoiceUrl or the call will fail.
Make sure you submit a fully qualified URL including:
- protocol (http:// or https://)
- file path
- properly url-encoded query parameters
Twilio must be able to reach this URL over the public Internet.