Hello,
Before the update, call transfer was working normally. The phone numbers we are trying to transfer to are numbers purchased via CloudTalk. The error message is as follows:
2026-03-19 09:06:46.222 call_223173ace44588bce3d2418be37 error: Error transferring call, SIP status code: 403 SIP error category: telephony_provider_permission_denied Error: twirp error unknown: unexpected status from INVITE response: sip status: 403: Caller ID is unauthorized. A Valid Caller ID is either a DID you have purchased from Twilio or a verified Caller ID.
From this error, I understand that I need to complete verification through Twilio, and I have already done that, but the error still persists. What else do I need to do?
Call ID: call_223173ace44588bce3d2418be37
Thank you for reaching out to Retell AI Support. We’ve received your ticket and our team will respond within 8 hours.
Hello,
The 403 error is being triggered by the Show Transferee As Caller option in your transfer config. When this is enabled, Retell uses the original caller’s phone number as the Caller ID on the outbound transfer leg. Since that number (ending in 6796 ) isn’t a Twilio-owned DID or verified caller ID in our Twilio account (not yours), Twilio rejects it.
Verifying it in your own Twilio account won’t help here — the outbound leg goes through Retell’s Twilio infrastructure.
Fix: In your agent’s transfer call configuration, remove Show Transferee As Caller option. The transfer will then use your Retell phone number as the Caller ID, which is authorized, and your transfers to CloudTalk numbers should work.
Regards,
Support Team @ Retell AI
