Twilio is unable to process the Content-Type of the provided URL. Please see Twilio's documentation on accepted content types for more information on valid Content-Types. You must return a Content-Type for all requests. Requests without a Content-Type will appear in the Debugger as a 502 Bad Gateway error.
- Having a phone number, outgoing call request or action attribute refer to a non-XML or audio resource.
- Having a Play verb attempt to play non-audio content, such as XML or text.
- Verify that that your web server is returning a Content-Type and it is the expected value
- Make sure the URL noted refers to a valid resource
- Make sure messages to or from your Twilio phone number are using a supported content-type. See the full list of supported content types.
- Use one of the supported request types to call a Twilio function.