# 12300: Invalid Content-Type

Log Type: APPLICATION

Log Level: ERROR

## Description

Twilio is unable to process the `Content-Type` of the provided URL. Please see Twilio's [documentation on accepted content types ](/docs/voice/twiml#twilio-understands-mime-types)for more information on valid `Content-Type`s.

You must return a `Content-Type` for all requests. Requests without a `Content-Type` will appear in the [Debugger](/console/runtime/debugger) as a 502 Bad Gateway error.

### Possible causes

* 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.

### Possible solutions

* 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](/docs/messaging/guides/accepted-mime-types).
* Use one of the [supported request types](/docs/serverless/functions-assets/functions/request-flow#supported-requests) to call a Twilio function.