### Answer The

telephony_provider_permission_denied

disconnection reason indicates that SIP trunk authentication failed. [(1) ]() Troubleshooting steps: 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. 2. If using custom telephony: - Double-check your configuration and ensure you imported the correct information - If the configuration is incorrect, delete the imported number and re-import - Verify your termination/origination settings in your SIP trunking provider [(2) ]() - Check the logs in your telephony provider and consider opening a ticket with them [(1) ]() 3. If using Telnyx via custom telephony: - Verify your SIP credentials are correct [(3) ]() - Try putting the username of the SIP trunk in the SIP header section when making the call 4. If using Retell-purchased numbers: - Make sure the destination number can accept the call — numbers purchased from Retell can currently only make calls to US numbers [(1) ]() Could you share: - Are you using custom telephony or Retell-purchased numbers? - What telephony provider are you using? - A call ID so the issue can be investigated further?

​ 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) [[3] " telephony permission denied" coming up again and again](https://discord.com/channels/1186424376300679209/1448951505431560276) ​

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