Based on your description, since calls aren’t appearing in your Retell Call History despite the SIP trace showing Retell receives the INVITE and responds with 100 Trying → 180 Ringing, this points to a configuration issue on the inbound side(1).
For Telnyx SIP trunk integration with inbound calls, verify these critical settings(1):
Origination URI Configuration
Your Telnyx origination settings must point to Retell’s SIP server. The SIP server URI is sip:sip.retellai.com(1). For TCP transport specifically, the URI should be sip:sip.retellai.com;transport=tcp(1).
IP Whitelisting
Ensure Telnyx accepts traffic from Retell’s IP blocks(1):
18.98.16.120/30(All regions)(1)143.223.88.0/21(United States traffic)(1)161.115.160.0/19(United States traffic)(1)
Authentication
If you’re using SIP trunk authentication, the username and password must match exactly what’s configured in Retell’s portal(2).
Number Import Verification
When you imported your number, ensure you provided the correct termination URI (for outbound, which you mentioned works) and that the inbound agent assignment is properly saved(1).
Since outbound works but inbound doesn’t, and calls don’t appear in Call History at all, the issue is likely in your Telnyx origination configuration rather than a cached routing issue on Retell’s side(1). Double-check your Telnyx origination settings to ensure calls are being routed to sip:sip.retellai.com;transport=tcp(1).
If the configuration appears correct, check with Telnyx support to verify there are no errors on their side(3). You can also reach out for additional support: