### Answer Here are the most common causes for Twilio SIP trunk outbound issues: 1. Username vs Friendly Name confusion [(1) ]() The username is different from the friendly name that shows in the credential list. Double-check you're using the actual username, not the friendly name. 2. Termination SIP URI issues - Check if there's a space in your Termination SIP URI—remove any spaces - Use a localized termination URI near your region (check [Twilio's localized URI docs]() ) 3. Authentication setup For your elastic SIP trunk to accept outbound requests, you need to either: - Whitelist IP addresses, OR - Create auth with username and password If you chose credentials, you must supply both the username and password when importing the number to Retell. 4. Check call logs for specific errors [(2) ]() Look at your call history for the disconnection reason. Common auth-related errors: -

telephony_provider_permission_denied

— SIP trunk credentials are not authenticated -

dial_failed

— Dialing failed (could indicate credential issues) 5. Verify the error message [(3) ]() One user saw this specific error:

"server required auth, but no username or password was provided"

— this confirms credentials weren't passed correctly to Retell when importing the number. Can you share the exact error or disconnection reason you're seeing in your call logs?

​ To learn more, see the sources I considered: [[1] Twilio](https://docs.retellai.com/deploy/twilio) [[2] Debug call disconnection](https://docs.retellai.com/reliability/debug-call-disconnect) [[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.

### Answer The

telephony_provider_permission_denied

error with a 403 Forbidden and SIP cause code 21 indicates that the SIP trunk authentication failed between Retell and Twilio. [(1) ]() [(2) ]() For Twilio specifically, here's what to check: 1. Verify you're using the correct username — In Twilio, the credential list shows a "Friendly Name" which is different from the actual "Username." Make sure you're entering the Username, not the Friendly Name, when importing the number to Retell. 2. Delete and re-import the number — If the configuration is incorrect, delete the imported number from Retell and re-import it with the correct credentials. [(1) ]() 3. Check with Twilio — If re-importing doesn't work, check your Twilio console for errors on their side. The 403 error confirms Twilio is rejecting the authentication. 4. Verify your Twilio SIP trunk setup: - Ensure your Termination SIP URI has no spaces - Confirm the credential list is properly attached to your SIP trunk - Make sure the username/password combination is correct Would you be able to verify the username vs friendly name distinction in your Twilio credential list? That's the most common cause of this specific error with Twilio.

​ 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) ​

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

### Answer Since you've verified the username/friendly name distinction multiple times and are still getting

telephony_provider_permission_denied

with a 403 error, here are additional steps: Next troubleshooting actions: 1. Delete and re-import the number — Even if you've entered credentials correctly before, delete the imported number from Retell and re-import it fresh with the credentials. [(1) ]() 2. Check with Twilio directly — Since the 403 confirms Twilio is rejecting the authentication, check your Twilio console logs to see the specific error on their side. 3. Verify Twilio credential list attachment — Ensure the credential list is properly attached to your SIP trunk in Twilio's console. 4. Check Termination SIP URI — Confirm there are no spaces in your Termination SIP URI, and consider using a localized termination URI near your region. If none of these resolve it, I'd recommend reaching out to Retell support directly with your Org ID (found in the bottom left of your dashboard under account settings) so they can investigate your specific configuration. For support: - Visit [Contact Sales]() - Visit [) Would you like me to help with anything else, or would you prefer to escalate this to human support?

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

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) ​

### Answer Aangezien je de configuratie meerdere keren hebt gecontroleerd en nog steeds

telephony_provider_permission_denied

met een 403-fout krijgt, raad ik aan om dit te escaleren naar Retell support. Volgende stappen: 1. Verwijder het nummer en importeer het opnieuw — Als de configuratie niet correct is, verwijder het geïmporteerde nummer en importeer het opnieuw. [(1) ]() 2. Neem contact op met je telefonieprovider — Controleer bij Twilio wat de exacte fout aan hun kant is. 3. Escaleer naar Retell support — Aangezien je dit al uitgebreid hebt geprobeerd, is het tijd om direct hulp te krijgen. Deel je Org ID (te vinden linksonder in je dashboard onder account settings) zodat ze je specifieke configuratie kunnen onderzoeken. Voor support: - Bezoek [Contact Sales]() - Bezoek [)

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

### Answer Ik zie dat je al meerdere keren de configuratie hebt gecontroleerd. Op basis van de beschikbare bronnen zijn hier de laatste opties: Stappen om te proberen: 1. Verwijder het nummer en importeer opnieuw — Verwijder het geïmporteerde nummer in Retell en importeer het opnieuw met de juiste credentials. [(1) ]() 2. Controleer bij Twilio — Vraag Twilio om de exacte foutmelding aan hun kant te bekijken. Om je Workspace ID te vinden (voor support) : - Ga naar je workspace settings pagina in het dashboard [(2) ]() Voor verdere hulp: - Bezoek [Contact Sales]() - Bezoek [) Interessant: een andere gebruiker meldde recent vergelijkbare

telephony_provider_permission_denied

fouten die uiteindelijk een bug aan Retell/Telnyx kant bleek te zijn — het probleem werd door het Retell team opgelost nadat ze de Org ID en call IDs ontvingen. [(3) ]() Kun je je Org ID en een paar Call IDs (van mislukte en geslaagde calls naar hetzelfde nummer) hier delen? Dan kan het support team dit onderzoeken.

​ To learn more, see the sources I considered: [[1] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[2] Workspace](https://docs.retellai.com/accounts/workspace) [[3] telephony_provider_permission_denied](https://discord.com/channels/1186424376300679209/1442577644574216433) ​

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

### Answer Bedankt voor het delen van je Org ID en Call IDs. Dit is precies wat het Retell support team nodig heeft om je specifieke configuratie te onderzoeken. Helaas kan ik als AI-assistent niet direct in je account kijken of tickets aanmaken. Je moet deze informatie delen met het Retell team: Org ID:

org_WXXT5hhzixUlfZeq

Call IDs: -

call_ea7c2d0c1202efbc819fd2a280e

-

call_791b6a67200e1aebc62d7b95d39

Volgende stappen: 1. Neem contact op met Retell support via [Contact Sales]() en deel bovenstaande gegevens. [(1) ]() 2. Controleer ook bij Twilio wat de exacte foutmelding aan hun kant is — de 403 error komt van Twilio die de authenticatie afwijst. Een andere gebruiker met vergelijkbare

telephony_provider_permission_denied

fouten ontdekte dat het uiteindelijk een bug aan de Retell/provider kant was, die door het team werd opgelost nadat ze de Org ID en Call IDs ontvingen. [(9) ]()

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

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

Appreciate the feedback! Feel free to ask me again with additional guidance or context.

### Answer De

403 Forbidden

met SIP cause code 21 bevestigt dat de SIP trunk authenticatie mislukt — dit betekent

telephony_provider_permission_denied

. [(1) ]() Je hebt je Org ID en Call IDs al gedeeld: - Org ID:

org_WXXT5hhzixUlfZeq

- Call IDs:

call_ea7c2d0c1202efbc819fd2a280e

,

call_791b6a67200e1aebc62d7b95d39

Aangezien je de credentials meerdere keren hebt gecontroleerd, moet dit nu door het Retell team worden onderzocht. Een vergelijkbare case met Twilio toonde aan dat de trunk credentials opnieuw moesten worden bijgewerkt — nadat de gebruiker nieuwe credentials aanmaakte en deze in Retell bijwerkte, werkte het. [(2) ]() Actie: Neem contact op met Retell support via [Contact Sales]() met bovenstaande gegevens, of wacht tot een teamlid hier reageert.

​ To learn more, see the sources I considered: [[1] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[2] Call transfer issues](https://discord.com/channels/1186424376300679209/1448419625401450696) ​

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