### Answer This issue typically stems from Elastic SIP Trunk configuration problems. Here's what to check: *1. Verify Termination Setup (for outbound calls) * [(1) ]() - Ensure your termination SIP URI has no spaces - Use a localized termination URI near your region 2. Check Authentication - If you set up auth via credentials, make sure you entered the correct username and password when importing the number to Retell - Note: the username is different from the "friendly name" shown in Twilio's credential list *3. Verify Origination Setup (for inbound calls) * - Set Retell's SIP server address as the origination SIP URI:

sip:sip.retellai.com

4. General Settings [(2) ]() - Ensure "Code Transfer" is enabled on your trunk - Ensure "Enable PSTN Transfer" checkbox is ticked 5. Check Twilio Call Logs [(3) ]() - Review Twilio call logs to see if calls are reaching Twilio first—if they're not making it to Retell, the issue is likely in your Twilio SIP trunk configuration A similar issue was resolved when users discovered they hadn't passed SIP trunk auth credentials into Retell properly. If outbound works but inbound doesn't (or vice versa) , double-check the corresponding termination/origination URI settings. [(1) ]()

​ To learn more, see the sources I considered: [[1] Twilio](https://docs.retellai.com/deploy/twilio) [[2] Retell AI - Connect to your own Twilio - Using Sip Trunking]() [[3] Issue with Inbound Voice Agent](https://discord.com/channels/1186424376300679209/1413628905235021887) ​

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