13255: Dialing .sip.twilio.com addresses is not currently allowed

This warning appears when your application tries to dial a .sip.twilio.com destination in a call flow that does not support internal SIP routing. Use <Dial><Sip> to send a call to your own SIP infrastructure. If you are calling a registered SIP endpoint on a Twilio SIP Domain, dial the endpoint's full Address of Record, such as username@yourdomain.sip.twilio.com.

• You attempted to dial a Twilio SIP Domain directly from a Twilio phone number or an active call.
• You used a bare SIP Domain such as yourdomain.sip.twilio.com instead of a full registered endpoint address such as username@yourdomain.sip.twilio.com.
• You attempted to route a SIP call between Twilio SIP Domains instead of to an external SIP endpoint or a registered SIP endpoint.

• If you need to send the call to your SIP infrastructure, update your TwiML or REST API request to dial your own SIP URI with <Dial><Sip>.
• If you need to reach a registered SIP endpoint on a Twilio SIP Domain, use the full Address of Record in the destination, such as username@yourdomain.sip.twilio.com.
• Verify that the username in the SIP URI matches a SIP endpoint that is currently registered on your SIP Domain.
• Replace unsupported .sip.twilio.com destinations that do not identify a registered SIP endpoint.

• Use SIP with Twilio Voice
• SIP Registration
• TwiML Voice: <Sip>