13252: Dial: Invalid header name

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.

• 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.

• 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.

• TwiML Voice <Sip>
• Outbound - Receiving SIP from Twilio
• Inbound - Sending SIP to Twilio