### Answer I understand your frustration. Since you mentioned "Simpano" (which appears to be a custom SIP trunk setup) , let's focus on the most common SIP trunking issues that cause outbound call failures. Critical SIP Trunking Checks: 1. Verify Your Termination URI [(1) ]() Your termination SIP URI must be correct and properly formatted. For Twilio elastic SIP trunks, it should end with

.pstn.twilio.com

. Check that there are no spaces in your termination URI . 2. Authentication Credentials [(2) ]() [(1) ]() If you're using username/password authentication, verify you entered the correct credentials when importing the number to Retell . The username is NOT the friendly name shown in the credential list—it's a different value you need to double-check [(1) ]() . *3. IP Whitelisting (if not using auth) * If you opted for IP whitelisting instead of credentials, you need to whitelist all IP addresses in the required ranges . Retell's SIP server does not have a static IP, so you must whitelist the entire IP range . 4. International Calling Permissions If calling outside the US, search for "geo" in your telephony provider settings to find "Voice Geographic Permissions" . Select "Elastic Sip Trunking" and enable the countries you want to dial . 5. Phone Number Format [(3) ]() Ensure your

to_number

is in proper E.164 format (e.g.,

+12137774445

) . Diagnostic Steps: Get your call ID from the failed attempts and check the

disconnection_reason

field, which will show exactly why calls are failing (e.g.,

dial_failed

,

sip_routing_error

,

telephony_provider_permission_denied

) [(4) ](

m/t/outbound-phone-call-not-connecting/249) . Next Steps: Check your SIP trunk logs in your telephony provider's console to see if they're receiving the outbound requests from Retell [(1) ]() . This will tell you if the issue is with the connection to your provider or with your provider's configuration. If the issue persists after these checks, please share a call ID from a failed attempt so we can provide more specific guidance.

​ To learn more, see the sources I considered: [[1] Twilio](https://docs.retellai.com/deploy/twilio) [[2] Import Phone Number](https://docs.retellai.com/api-references/import-phone-number) [[3] Outbound Calls (Make Calls)](https://docs.retellai.com/deploy/outbound-call) [[4] Outbound Phone Call Not Connecting](https://community.retellai.com/t/outbound-phone-call-not-connecting/249) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.