### Answer The

telephony_provider_unavailable

disconnection reason indicates that the telephony provider is not available or has errors on their side. [(1) ]() ## Troubleshooting Steps 1. Check Call History Logs Review the call history and detailed log in your Retell dashboard. It contains the disconnection reason, SIP error code, and error message which can help identify the root cause. *2. If Using Custom Telephony (SIP Trunking) * - Double-check your SIP trunk configuration and ensure you imported the correct information. - Verify your termination settings in your SIP trunking provider (e.g., Twilio) . [(2) ]() - If the configuration appears incorrect, delete the imported number and re-import it. [(1) ]() - Check the logs in your telephony provider's dashboard and consider opening a ticket with them. [(2) ]() 3. If Using Numbers Purchased from Retell - Ensure the destination number can accept the call. Currently, numbers purchased from Retell can only make calls to US numbers (unless using international calling to the 14 supported countries) . [(1) ]() 4. Authentication Check If you're using Twilio SIP trunking, verify your termination URL and authentication credentials are correctly configured in Retell. [(2) ]() Since direct Twilio API calls work but Retell calls fail, the issue likely lies in the SIP trunk configuration between Retell and Twilio. I'd recommend checking your Twilio SIP trunk termination settings and ensuring the credentials match what you've imported into Retell. For specific call ID investigation, you'll

need to reach out to Retell support directly as I cannot access internal call logs.

​ To learn more, see the sources I considered: [[1] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[2] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) ​

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