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

### Answer A

dial_failed

disconnection reason typically indicates issues unrelated to billing. According to the documentation,

dial_failed

represents "cases where sip error codes are not available, or error is unknown." [(1) ]() If billing were the issue, you'd likely see

no_valid_payment

as the disconnection reason, which indicates "no valid payment registered on file, or service shut down due to bill overdue." [(2) ]() Common causes for

dial_failed

include: - Phone number marked as spam by carriers (especially with high outbound volume or low pickup rates) [(1) ]() - Telephony provider configuration issues - If using Twilio, you may need to verify your customer profile and assign the phone number to it [(3) ]() Steps to troubleshoot: 1. Check the call history and detailed log for the SIP error code and error message [(1) ]() 2. If using custom telephony, double-check your configuration and credentials 3. If using numbers purchased from Retell, ensure the destination number can accept calls (Retell numbers can currently only call US numbers) I don't have specific information about Retell's billing cycle in my sources. For billing-related questions, you may want to reach out to Retell support directly.

​ 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] OUTBOUND CALLS FAILING](https://discord.com/channels/1186424376300679209/1370279738081542215) ​

@AI Evy i keep getting dial failed whats the cause of that ?

number with Retell's spam remediation feature (verified phone number)

​ To learn more, see the sources I considered: [[1] Debug outbound connection issues](https://docs.retellai.com/reliability/debug-outbound-call) [[2] dial failed - Error](https://discord.com/channels/1186424376300679209/1357414439808270386) [[3] Getting dial failed.](https://discord.com/channels/1186424376300679209/1334589096387149884) ​

### Answer The

dial_failed

disconnection reason represents cases where SIP error codes are not available, or the error is unknown. [(1) ]() Common causes include: - Invalid destination number (number doesn't exist) [(2) ]() - Number marked as spam by carriers [(1) ]() , [(2) ]() - Telephony provider errors (like max calls per second limit reached) - Geographic restrictions (Retell-purchased numbers can only call US numbers) [(1) ]() , [(2) ]() - Configuration issues with custom telephony (incorrect outbound termination URL or credentials) - The destination number is blocking your calls [(3) ]() Steps to troubleshoot: 1. Check the call history and detailed log—it contains the disconnection reason, SIP error code, and error message [(1) ]() 2. If using custom telephony: - Double-check your configuration and ensure you imported the correct information - If configuration is incorrect, delete the imported number and re-import - Check with your telephony provider to see what error is on their side 3. If using numbers purchased from Retell: - Ensure the destination number can accept calls - Numbers purchased from Retell can currently only make calls to US numbers If your number is being marked as spam: - Purchase a new number and warm it up before sending high traffic (slowly add outbound traffic) - Increase pickup rate - Register the

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] 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.

### Answer The error message clearly indicates an authentication issue with your SIP trunk configuration: >

server required auth, but no username or password was provided

This means your telephony provider requires authentication credentials, but they weren't supplied when importing the number to Retell. [(1) ]() To fix this: 1. Delete the imported number from Retell 2. Re-import the number with the correct credentials—when importing, supply the termination SIP URI along with the username and password for authentication [(2) ]() 3. Double-check that the username is correct (note: the username is different from the friendly name in Twilio) If you're using Twilio with elastic SIP trunking, ensure you've configured authentication either via IP whitelisting or username/password credentials in your termination settings.

### Answer The

telephony_provider_permission_denied

error with SIP status code 403 indicates that SIP trunk authentication failed. [(1) ]() , [(2) ]() Common causes and fixes for Twilio: 1. Incorrect credentials — Verify the username and password you entered in Retell match your Twilio trunk credentials. Note: the username is not the friendly name shown in the credential list—you need the actual username. [(3) ]() 2. Check your Termination SIP URI — Remove any spaces if present, and use a localized termination URI near your region. 3. Geographic permissions — If calling international numbers, go to Twilio and search "geo" to find "Voice Geographic Permissions," select "Elastic SIP Trunking," and enable the countries you want to dial. 4. Re-import with correct credentials — Delete the imported number from Retell and re-import it with the correct username and password. A similar issue was resolved by creating new credentials and updating them in Retell. [(4) ]() Steps to verify in Twilio: - Go to your Elastic SIP Trunk → Termination settings - Confirm authentication is properly configured (either IP whitelist or username/password) - If using credentials, double-check the actual username (not the friendly name) [(3) ]() Since the 403 error comes from Twilio's side, you may also want to check your Twilio console for any additional error details. [(5) ]()

​ 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] Twilio](https://docs.retellai.com/deploy/twilio) [[4] Call transfer issues](https://discord.com/channels/1186424376300679209/1448419625401450696) [[5] I keep getting SIP status code: 403 SIP error category: telephony_provider_permission_denied Error](https://discord.com/channels/1186424376300679209/1389628288137429032) ​

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