---
page_type: error
code: 12300
message: "12300: Invalid Content-Type"
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-Types.

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/sms/accepted-mime-types).
- Use one of the [supported request types](/docs/runtime/functions/request-flow#supported-requests) to call a Twilio function.