Hi Retell team, I’m on Pay As You Go with a Twilio number connected via custom telephony (+13158563314). Inbound calls work perfectly. Cold transfers to a US number (+13158563313, SIP INVITE, static destination) consistently fail with: “Transfer call cannot be completed, probably don’t have the permission to perform the transfer.” Twilio shows no record of the transfer leg, so it’s being rejected before leaving Retell. I’ve completed identity verification for outbound calls and I’m off the free trial. Per similar threads, could you please enable outbound calling / telephony access on my account? Recent failing call ID: call_cba158347accd915a9d…115 (Jul 10, 1:48 PM ET — full ID in my call history).
Hey @heyhank101 can you share the full Call ID here ?
Thank You
call_96a03c5e318bb836f8255b38517
call_cba158347accd915a9ded5ce115
@heyhank101 Reported to the team for a review.
We will get back to you as soon we have an answer.
Thank You
Hey @heyhank101 On BYOC / custom telephony, Retell doesn’t gate outbound; the transfer INVITE is going out to your own Twilio Elastic SIP Trunk, and Twilio is returning SIP 403 Forbidden on both failing calls. The INVITE is rejected at your trunk’s termination edge before it becomes an outbound call.
A few things to check on the Twilio dashboard:
- IP Access Control Lists: your trunk has no SIP digest credentials configured, so it’s IP-ACL only. Retell’s SIP egress IP ranges need to be on that ACL. The current egress IPs are documented in our documentation (link below).
- Voice Geographic Permissions on the Twilio project that owns the trunk, confirm the United States is enabled for outbound. A geo-permission block also surfaces as a 403 at termination.
- Termination attributes: confirm outbound calling is enabled on the trunk and that your number is one of the origination numbers attached to it (not just for inbound).
Custom Telephony guide: Connect Retell voice agents to custom telephony - Retell AI
Twilio guide: Twilio - Retell AI
Thank You