Hi — I have a similar issue to this post: Reset the Inbound SIP Routing
Inbound calls to my Telnyx SIP trunk number ring but the agent never picks up. Outbound calls work perfectly with the same agent.
SIP trace confirms Retell receives the call:
- INVITE reaches sip.retellai.com
- Retell responds 100 Trying → 180 Ringing
- Retell never sends 200 OK
- Call never appears in my Retell Call History
Setup:
- Provider: Telnyx (FQDN connection, SRV DNS, TCP transport)
- Termination URI: sip.telnyx.com
- Number imported as custom telephony
- Inbound agent is assigned (D.O.N.N.A. v.4/V2)
- I recently updated the agent from v.3 to v.4 — could this be a cached routing issue like the post linked above?
Org: saiago business llc workspace
Can someone from the team check if my inbound SIP routing needs to be reset? Happy to share the full SIP trace.
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:
Hello @saiagobusinessllc
Can you share your org id (settings → workspace )
and the pcap file from your provider for this call
I’m sorry, but as an AI Assistant knowledgeable about Retell AI, I only have the ability to answer questions about Retell AI.
If you’re experiencing issues with SIP trunking and need to share diagnostic information with Retell support, you can find your workspace ID (org ID) by following these steps(1):
- Navigate to the workspace settings page in your dashboard
- Click the workspace selector in the top left corner
- Your workspace ID will be displayed in the settings
For SIP-related troubleshooting, you may also want to provide your telephony provider’s PCAP file, which contains detailed call signaling information(2)(3).
Hi Omar, thanks for looking into this.
Org ID: org_lKEJNGFA9MuoYwLN
I don’t have a pcap file, but I do have the full SIP Call Flow text export from Telnyx showing the complete INVITE → 100 Trying → 180 Ringing → CANCEL → 487 sequence. The key details from the trace:
- Telnyx sends INVITE to sip:16316857178@sip.retellai.com via TCP on port 5060
- Retell (18.98.16.123) responds 100 Trying then 180 Ringing repeatedly
- Retell never sends 200 OK
- Caller hangs up, Retell returns 487 Request Terminated
- Call never appears in my Retell Call History
I can share the full CDR text if that helps. Would you like me to upload it here?
Hello @saiagobusinessllc
I see your phone number is not in the correct format
Please reconnect it and use e.164 format
+18888888888
No dash or spaces in between