### Answer The

telephony_provider_permission_denied

disconnection reason indicates that SIP trunk authentication failed. [(1) ]() [(2) ]() This issue has been reported by other users as intermittent/random, where calls would fail with this error but succeed on retry—even without any configuration changes. [(3) ]() What was discovered: - One user reported that ~10% of dials suddenly started failing with this error across multiple organizations, different numbers, and different agents - The issue was not related to specific numbers, accounts, or the TCP/UDP outbound transport setting - Recalling the same number often succeeded on the second or third attempt - The Retell team identified and fixed a bug that was causing this Troubleshooting steps: 1. Check your call history and detailed log for the SIP error code and error message [(1) ]() 2. If using custom telephony (Twilio/Telnyx) : - Double-check your SIP trunk configuration is correct - Verify your termination SIP URI has no spaces [(4) ]() - Confirm username and credentials are correct - Check with your telephony provider for errors on their side [(1) ]() 3. If the issue persists across multiple numbers/orgs with no configuration changes, this may be a platform-level issue—consider reporting it in the

#❓・bug-report

channel with your Workspace ID and example call IDs (one working, one failed to the same destination) . [(3) ](

6300679209/1442577644574216433)

​ 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] telephony_provider_permission_denied](https://discord.com/channels/1186424376300679209/1442577644574216433) [[4] 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) ​

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