### Answer The

telephony_provider_permission_denied

disconnection reason indicates that the SIP trunk authentication failed. [(1) ]() [(2) ]() Steps to troubleshoot: 1. Check the call history and detailed log — it contains the disconnection reason, SIP error code, and error message, which should help identify the root cause. [(1) ]() 2. If using custom telephony (e.g., Twilio, Telnyx via SIP trunk) : - Double-check your configuration and ensure you imported the correct information. - Verify your Termination SIP URI has no spaces. [(3) ]() - Confirm your username and credentials are correct (the username is different from the friendly name) . - If the configuration is incorrect, delete the imported number and re-import. [(1) ]() - Check with your telephony provider (Twilio, Telnyx, etc.) to see what error is on their side. 3. Common provider-specific issues: - For Telnyx, errors like "Telnyx error 403 Unverified origination number" indicate you need to contact Telnyx directly. [(4) ]() - For Twilio, ensure your number isn't flagged or blacklisted, and verify inbound calls work correctly. [(5) ]() 4. If using numbers purchased from Retell, ensure the destination number can accept the call. [(1) ]() Could you share: - Whether you're using a Retell-purchased number or custo

m telephony (Twilio/Telnyx) ? - The call ID from a failed attempt so the logs can be reviewed?

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

​ To learn more, see the sources I considered: [[1] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[2] Debug call disconnection](https://docs.retellai.com/reliability/debug-call-disconnect) [[3] I’m trying to use a toll-free number (connected from Twilio through a SIP trunk)](https://retell.discourse.group/t/i-m-trying-to-use-a-toll-free-number-connected-from-twilio-through-a-sip-trunk/127) [[4] telephony_provider_permission_denied](https://discord.com/channels/1186424376300679209/1449059903175131196) [[5] Outbound sip call getting Telephony_provider_permission_denied error](https://discord.com/channels/1186424376300679209/1433144721429106738) ​