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Hi Retell Support,
# ❓・bug-report
n
Hi Retell Support, We’re experiencing a persistent inbound calling issue via Twilio Elastic SIP Trunk. Observed Behaviour: • Calls ring briefly • Caller hears “Sorry, the person you're calling is on another call” • Twilio logs show Busy (0 sec duration) • SIP trace shows: INVITE → Ringing → SIP/2.0 603 Rejected This occurs consistently. Environment: • Twilio Elastic SIP Trunk • Origination SIP URI: sip:sip.retellai.com • Transport tested: TCP / TLS • Twilio number: UK (+44) • Call routing region: US1 • Agent Type: Conversation Flow Agent • Concurrent Calls Limit: 20 Important Findings: • SIP signalling successfully reaches Retell • Retell responds with Ringing • Retell then rejects call with 603 Rejected This indicates the call is not failing at Twilio or network level. Troubleshooting Already Performed: • Verified Twilio trunk configuration • Verified Origination URI • Tested TCP / TLS transport • Created brand new test agents • Rebound phone number to fresh agents • Verified concurrency limits • Confirmed no visible active calls in dashboard Issue persists. Suspected Cause: Possible stale / stuck SIP session or telephony presence lock at: • Phone number routing layer • Agent presence state • Account session state Request: Could you please investigate and, if necessary: • Clear active SIP sessions • Reset telephony presence / agent availability state • Reset phone number routing state • Confirm rejection reason for 603 responses Retell Account Email: [your login email] Agent ID: agent_12313fb9b5d7d67639bf164541 Phone Number: +447427914908 Example Twilio Call SID: CAa8cb2cdc57ab80d1e3f00a876ed7da4c Happy to provide additional PCAPs if required. Thanks in advance. Best regards, Craig
email is luvio.limited@gmail.com
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Hi @Nythix
I report this issue to team to look at
n
thanks, will you reply here or email?#
@Shah - support @ Retell AI
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@Nythix Once there's a reply me or other support member will reach out to you here
Hi @Nythix can you provide a call id and pcap file
n
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@Nythix Please provide the retell call id and this pcap file is empty
n
I cannot find a corresponding Retell Call ID for this call. Twilio Call SID: CAa8cb2cdc57ab80d1e3f00a876ed7da4c The call does not appear in my Retell call logs (only web_call sessions are visible). Please confirm whether this SIP request reached Retell’s edge and if it was rejected before session creation. Now when I call the number it doesn't connect at all https://cdn.discordapp.com/attachments/1476589717175799858/1476700442951024671/call-log-CAa8cb2cdc57ab80d1e3f00a876ed7da4c.pcap?ex=69a213f5&is=69a0c275&hm=6fe9b63772d4c27fb5ff1d2354549df4fc39113ac378e1d7cf6864db28d550c5&
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Twilio Call SID: CAfa82347a6ccc918a00f50c2691decdb8 Trunk SID: TKd56b90319f07c6d54d17d5a3b9c9dcf1 SIP URI Used: sip:agent_12313fb9b5d7d67639bf164541@sip.retellai.com;transport=tls Result: Twilio status: No Answer Duration: 0 seconds No Retell call generated in Call History Inbound agent assigned under Custom Telephony
Retell is not returning 200 OK to Twilio INVITE. Can you confirm if the agent ID is properly registered for SIP routing on your backend?
@Shah - support @ Retell AI @Shehroze -Support @Retell
Retell phone number: +447427914908 (shown as +44 7427 914908 in UI) Provider: Custom telephony Inbound Call Agent assigned: Conversation Flow Agent 2 / V13 Agent ID used in Twilio origination URI: agent_12313fb9b5d7d67639bf164541 (confirmed matches agent) Twilio Elastic SIP Trunk: TKd56b90319f07c6d54d17d5a3b9c9dcf1 (US1) Example Twilio Call SID: CAfa82347a6ccc918a00f50c2691decdb8 Twilio shows: Direction Trunking Originating, Type sip-pstn, Status No Answer, Duration 0s Retell Call History shows no custom_telephony calls created (only web_call) SIP PCAP not available (need guidance where to enable / whether you can provide server-side logs) Question: Can you check on your side why INVITEs to sip:agent_123...@sip.retellai.com;transport=tls are not creating a call session? Is there an account/verification/telephony enablement gate, or a region mismatch (Twilio US1) preventing inbound SIP acceptance?
c
Duplicate ticket please check the other
o
Hello I checked your org , 1- You still have spaces in your phone number 2- How you got this SIP URI with the agent id in it ? 3- the correct one is sip:sip.retellai.com please follow this docs https://docs.retellai.com/deploy/twilio
n
Hi team, Phone number spaces There are no spaces in the SIP signaling. In our Twilio SIP PCAP the INVITE is: INVITE sip:+447427914908@sip.retellai.com and the To: header is also: To: So the number is in E.164 format with no spaces. SIP URI with agent id We are not using an agent-id SIP URI anymore. We previously tested that format, but it’s removed now. Correct SIP URI Confirmed — Twilio trunk Origination is set to: sip:sip.retellai.com Current behavior on an inbound test call: SIP flow from PCAP: 100 Trying → 180 Ringing → 486 Rejected Twilio status shows Busy (0 sec duration) No session appears in Retell Call History Can you please check why the Retell SIP gateway is returning 486 Rejected for DID +447427914908 (Custom telephony) before a session is created, and whether there is any account-level inbound SIP enablement or routing lock needed? Attached again: Twilio SIP PCAP + Twilio Call SID: CA03acde4657fc92683eb1acef73d0d29c Thanks, Craig
Following your Twilio doc, we have Origination set to sip:sip.retellai.com and the +44 number moved onto the trunk. The SIP PCAP shows INVITE → 180 Ringing → 486 Rejected. Can you confirm whether our ‘import number’ configuration (Termination SIP URI + auth) is correct for this DID, and why the SIP edge returns 486 before creating a call session?
Agent has now answered thanks for your help
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