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I'm having an issue with a custom SIP trunk integr...
# ❓・ai-evy-support
y
@AI Evy I'm having an issue with a custom SIP trunk integration and need some help. I'm using Maqsam as my telephony provider connected to Retell via a custom SIP trunk. The setup is: • Termination URI: sip.retellai.com • SIP Username: scalepods • Transport: UDP (also tried TCP) The issue: When a user picks up the call, it rings briefly then gets disconnected. The call logs are updating on the Maqsam side but there are zero logs showing on the Retell side — it's like Retell never receives the call. Things I've already tried: • Switching transport from TCP to UDP • Double-checked SIP credentials
a
Thanks for tagging me @yashrao. I'll look through relevant sources and get back to you shortly.
### Answer Based on your description, here are several things to check: 1. Termination URI Format Your termination URI should include the 
sip:
prefix. The correct format is 
sip:sip.retellai.com
. [(1) ]() For specific transport methods, append the transport to the URI: - TCP: 
sip:sip.retellai.com;transport=tcp
- UDP: 
sip:sip.retellai.com;transport=udp
- TLS: 
sip:sip.retellai.com;transport=tls
2. IP Whitelisting Ensure your telephony provider (Maqsam) has whitelisted Retell's IP blocks for traffic: - 
18.98.16.120/30
(All regions) - 
143.223.88.0/21
(certain United States traffic) - 
161.115.160.0/19
(certain United States traffic) 3. Phone Number Format When importing your phone number to Retell, ensure it's in E.164 format (e.g., 
+14157774444
with the 
+
prefix and country code, no spaces or special characters) . [(2) ]() 4. Verify Number Import Since no logs appear on the Retell side, confirm that: - Your phone number is properly imported into Retell - An agent is bound to that number for handling inbound calls 5. Origination Settings For inbound calls not connecting, check your origination settings in your SIP trunking provider (Maqsam) and review their logs. [(1) ]() If the issue persists after these checks, I'd recommend opening a ticket with Maqsam to verify what's happening on their side, as the call logs updating there but not reaching Retell suggests the SIP traffic may not be routing correctly to Retell's servers.
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] SIP Trunk Outbound Call - No SIP INVITE reaching my server](https://community.retellai.com/t/sip-trunk-outbound-call-no-sip-invite-reaching-my-server/760) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
y
i have treid adding this sip:sip.retellai.com in termination url in retell but it shows internal server error also when i add this sip.retellai.com then it gets saved successfully
@AI Evy i have treid adding this sip:sip.retellai.com in termination url in retell but it shows internal server error also when i add this sip.retellai.com then it gets saved successfully
a
Thanks for the follow-up, @yashrao. I'll get back to you soon.
### Answer The behavior you're seeing is expected. When importing a phone number to Retell, the termination URI field should NOT include the 
sip:
prefix. [(1) ]() Looking at the Import Phone Number API documentation, the 
termination_uri
parameter example shows:
Copy code
"termination_uri": "someuri.pstn.twilio.com"
So 
sip.retellai.com
(without the 
sip:
prefix) saving successfully is correct. **Important clarification**: The 
sip:
prefix is used when configuring your telephony provider's origination settings (like Maqsam pointing to Retell) , not when importing the number into Retell's dashboard. [(2) ]() For your Maqsam → Retell inbound setup: - **In Maqsam's origination settings**: Point to 
sip:sip.retellai.com
(with prefix) - **In Retell's import number termination URI**: Use your Maqsam termination URI (without 
sip:
prefix) — this is for outbound calls from Retell to Maqsam Since you're not seeing any logs on Retell's side for inbound calls, the issue is likely in Maqsam's origination configuration. Verify that Maqsam is correctly routing inbound calls to 
sip:sip.retellai.com
.
​ To learn more, see the sources I considered: [[1] Import Phone Number](https://docs.retellai.com/api-references/import-phone-number) [[2] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
Thanks for the follow-up, @yashrao. I'll get back to you soon.
y
@AI Evy maqsam is already using this endpoint sip:sip.retellai.com.
a
### Answer Since Maqsam is already configured to point to 
sip:sip.retellai.com
but calls still aren't reaching Retell, here are additional items to verify: 1. Phone Number Import Verification Confirm the phone number is properly imported into Retell with an agent bound to it. [(1) ]() If the number isn't imported or no agent is assigned, inbound calls won't be processed. 2. Phone Number Format Ensure your phone number is imported in E.164 format with the 
+
country code prefix (e.g., 
+14157774444
) . [(2) ]() 3. Transport Method in Maqsam Try specifying the transport method explicitly in Maqsam's origination settings: [(1) ]() - For TCP: 
sip:sip.retellai.com;transport=tcp
- For UDP: 
sip:sip.retellai.com;transport=udp
TCP is recommended. 4. IP Whitelisting Verify Maqsam has whitelisted Retell's IP blocks: - 
18.98.16.120/30
(All regions) - 
143.223.88.0/21
(certain United States traffic) - 
161.115.160.0/19
(certain United States traffic) 5. Check Maqsam's Logs Since Retell shows zero logs, the SIP traffic may not be reaching Retell's servers at all. Review Maqsam's detailed SIP logs to see if the INVITE is being sent and what response (if any) is received. If all configurations appear correct, I'd recommend opening a support ticket with Maqsam to trace the SIP traffic path and confirm their origination is actually sending requests to Retell's SIP server.
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] SIP Trunk Outbound Call - No SIP INVITE reaching my server](https://community.retellai.com/t/sip-trunk-outbound-call-no-sip-invite-reaching-my-server/760) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
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