### Answer Here are some troubleshooting steps for inbound calls not connecting via Twilio Elastic SIP Trunking: ## Check Your Origination Settings For inbound calls, verify your origination configuration in Twilio. [(1) ]() The origination SIP URI should be set to Retell's SIP server address:

sip:sip.retellai.com

[(1) ]() [(2) ]() ## Verify Transport Method Make sure you're using a supported transport method. For different transports on inbound calls: [(1) ]() - For TCP:

sip:sip.retellai.com;transport=tcp

- For UDP:

sip:sip.retellai.com;transport=udp

- For TLS:

sip:sip.retellai.com;transport=tls

## Confirm Number Import Ensure the number was properly imported to Retell with the correct termination SIP URI. [(2) ]() If you configured auth via credentials, you need to supply the username and password as well. ## Check Agent Binding Verify that an

inbound_agent_id

is assigned to the imported number. If this is null, the number would not accept inbound calls. [(3) ]() ## Review Twilio Logs Check the logs in your telephony provider (Twilio) , and consider opening a ticket with them if the issue persists. [(1) ]() ## IP Whitelisting If you're using IP whitelisting, ensure you've whitelisted Retell's IP block:

18.98.16.120/30

(All regions) ,

143.223.88.0/21

(certain United States traffic) ,

161.115.160.0/19

(certain United States traffic) . If you continue having issues, check if the call appears in your Retell dashboard at all—if not, the issue is likely in the Twilio-to-Retell routing configuration.

​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Twilio](https://docs.retellai.com/deploy/twilio) [[3] Import Phone Number](https://docs.retellai.com/api-references/import-phone-number) ​

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