Call receptionist agent (Retell + Twilio) app error

Hey everyone,

I’m trying to connect our Twilio BYOC trunk (bci-tech-trunk.sip.twilio.com) with our Retell voice agent so it can answer incoming calls.

When we call the Twilio number, it connects but plays: “We’re sorry, an application error has occurred. Goodbye.”

Twilio’s logs show Error 11200 (HTTP 404) — “Cannot POST /v2/handle-call” fromhttps://api.retellai.com/v2/handle-call?agent_id=agent_7ce1************03d&retell_api_key=key_2***********049.I also tried switching it to GET, but the same issue happens.

We’ve checked all the Twilio settings — BYOC trunk, SIP domain, transport set to TLS, and tested /v2/handle-call, /v2/handle-call/twilio, and /v2/create-phone-call. Secure media has been tested on and off, same result.

Could someone confirm what the correct Twilio webhook endpoint should be for this setup, and whether inbound SIP from Twilio should authenticate via IP/TLS trust instead of credentials?

Troubleshooting I’ve Tried

Verified Twilio BYOC trunk and SIP domain setup
Tested both HTTP GET and POST
Tried multiple Retell endpoint paths (/v2/handle-call, /v2/handle-call/twilio, /v2/create-phone-call)
Confirmed origination target = sip:sip.retellai.com;transport=tls
Tested with Secure Media enabled and disabled
Retell webhook in place: https://bci-tech-trunk.pstn.twilio.com

Still getting the same “application error” message and 404 logs from Retell’s API.

Environment details: