# 13252: Dial: Invalid header name

Log Level: WARNING

## Description

Twilio raises this warning when your `<Dial><Sip>` request includes a SIP header name that Twilio cannot use. For custom headers, use the `x-` prefix. Twilio also supports `User-to-User`, `Remote-Party-ID`, `P-Preferred-Identity`, and `P-Called-Party-ID` without the `x-` prefix. Header names must also use characters that are valid for SIP so Twilio can generate a valid SIP message.

### Possible causes

* The header name contains characters that are not valid in a SIP header name.
* A custom header was added to the SIP URI without the required `x-` prefix.
* The header name is not one of the supported non-`x-` SIP headers for `<Dial><Sip>`.
* Escaped characters in the SIP URI changed the header name into an invalid format.

### Possible solutions

* Update the header name so it uses only SIP-safe characters. Header names should generally contain letters, numbers, and hyphens.
* For custom headers, rename the header with an `x-` prefix such as `x-customer-info`.
* If you need a standard SIP header, use one of the supported names exactly as documented: `User-to-User`, `Remote-Party-ID`, `P-Preferred-Identity`, or `P-Called-Party-ID`.
* Review the generated SIP URI and remove or correct any percent-escaped characters that altered the header name.

#### Additional resources

* [TwiML Voice `<Sip>`](/docs/voice/twiml/sip)
* [Outbound - Receiving SIP from Twilio](/docs/voice/api/receiving-sip)
* [Inbound - Sending SIP to Twilio](/docs/voice/api/sending-sip)