There is no username in the SIP URI when calling a SIP registered endpoint

Calling Twilio SIP domains such as "yourdomain.sip.twilio.com" is not allowed. You can only call a registered SIP endpoint such as "username@yourdomain.sip.twilio.com".

• Attempting to place a call from Twilio back to your own Twilio SIP domain. Twilio does not allow SIP calls between Twilio domains either in the same account or different accounts.
• Attempting to call a registered SIP AOR without specifying the username you wanted to call

• Add the correct username in the SIP URI you call, e.g., username@yourdomain.sip.twilio.com