Update sip-twilio.mdx

Author: sahilsuman933

fern/advanced/sip/sip-twilio.mdx

@@ -137,7 +137,7 @@ This guide walks you through setting up both outbound and inbound SIP trunking b
 
    ![Origination Settings](../../static/images/sip/sip-twilio-origination.png)
 
-   Add your Vapi SIP URI in the following format: `sip:YOUR_PHONE_NUMBER@sip.vapi.ai`, where "YOUR_PHONE_NUMBER" is your chosen SIP number that you will attach to this trunk.
+   Add your Vapi SIP URI in the following format: `sip:YOUR_PHONE_NUMBER@<credential_id>.sip.vapi.ai`, where "YOUR_PHONE_NUMBER" is your chosen SIP number that you will attach to this trunk.
 
    ![Origination Creation](../../static/images/sip/sip-twilio-origination-creation.png)