Outbound calling not working on custom Twilio SIP trunk, please enable outbound for my account

Support Help
1

Hi Retell team, I’m on Pay As You Go and have a custom Twilio Elastic SIP Trunk fully configured, Termination URI set to uk1.pstn.twilio.com, Origination URI set to sip:sip.retellai.com, credential list added, and my UK number +447863776931 imported successfully. Outbound calls are not connecting, the call just doesn’t go through with no error shown. Could you please enable outbound calling for my account? Thank you.

2

Hello @ompatel.astrixia Can you share your ORG ID ? and can you confirm for your Twilio Elastic SIP Trunk to accept Retell’s outbound requests, you must whitelist Retell’s SIP SBC CIDR block:

18.98.16.120/30

If you’re using credential-list auth instead, ensure the username/password is supplied when importing the number to Retell.

Thank You

3

If you believe you configured the phone number correctly. Check if you use the correct webhook URL to either n8n, Make or any workflow you built.

4

org_i4n4hmyQiGDC8qMj thats my org id and i can confirm that the sbc block has been whitelisted

5

Hi, I can see this has been marked as solved but I have not received any confirmation that outbound calling has been enabled on my account. Can you please confirm whether it has been approved and if not what steps are needed? My workspace ID is org_i4n4hmyQiGDC8qMj. Thank you.

6

Hey @ompatel.astrixia Checking with the team

7

Hi, just checking in on the outbound calling approval, any update from the team? Happy to provide any additional info if needed.

8

Hello @ompatel.astrixia

Looked at call_f8279adfbcf54a99eab43af60ae and ~7 similar outbound attempts from +447863776931 → +447436519663 over the last few days all failed at 0ms with telephony_provider_permission_denied.
Since you’re on BYOC (Twilio sub-account ACfb129418ca13900b597297b3a8bba532), Retell forwards the INVITE to your trunk and your trunk is rejecting it with a SIP 401/403. The block is on your Twilio side there’s nothing to toggle on Retell.
Please check, on the sub-account owning the Elastic SIP Trunk:

  1. UK outbound voice permissions enabled (on both sub-account and master if applicable).
  2. +447863776931 attached to the Trunk’s Numbers tab and verified as a Caller ID.
  3. Termination auth - Credential List username/password match what’s in your Retell BYOC config, or IP ACL allowlists Retell’s SBC range.
  4. Sub-account balance / international voice billing active.

Open Twilio Voice Debugger around 2026-06-08 06:54:51 UTC and share the error code that’ll tell us which of the four it is.

Thank You