hey guys, can please sombody help me with zendesk integration? (twilio runs under it) When I try to forward to the given SIP-IN, it just simply puts the phone down and I have no info about what is happening. I checked the logs in vapi it just says the tool was called, but no error, only phone put down.

Thanks for reaching out! To help troubleshoot, could you clarify what type of call transfer you’re attempting (for example, phone-to-SIP, SIP-to-SIP, or another scenario)? Some transfer types are not supported and may cause the call to drop immediately. This will help me guide you to the right solution. Source: - [Debug call forwarding drops](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops)

SIP to SIP

Hi, could you please provide a call id where you experienced this issue? We would like to review the logs to identify the cause.

Hi, yes of course. A couple of examples: 019a93be-3220-7116-95cd-2684fa4a096a 019a93be-3220-7116-95cd-2684fa4a096a 019a93b5-f166-799c-8e4a-4d06f0245d77 019a93a4-4078-766b-8bfc-08f2259097c6| i have also attached the files and email i have sent to zendesk (it contains a bit about vapi too) " We're attempting to transfer active calls from our Twilio-based phone system to our Zendesk Talk agents via the SIP endpoint nexteam-zendesk.sip.twilio.com. We've implemented three different transfer methods (detailed in the attached documentation), and all encounter the same issue: successful authentication followed by 403 Forbidden authorization failure. The attached documentation includes: - Complete proxy infrastructure details (Asterisk on 104.236.222.212) - All three transfer method implementations - SIP packet captures showing authentication flow - Specific questions about endpoint configuration Our source IP 104.236.222.212 is whitelisted in Zendesk SIP-IN settings. Credentials (andrew/Triotro44404) appear to authenticate successfully but lack authorization. Please review Section 5 of the documentation for our specific questions. " https://cdn.discordapp.com/attachments/1440330123298607276/1441390141548789921/zendesk-support-package.tar.gz?ex=6925932d&is=692441ad&hm=ab2d88f770b84a0fabcaf5710770049ac4e33109639f627b8665660b13b4cd93&

Hi there, Thanks for sharing the PCAP — I reviewed the capture, and the root cause of the 403 Forbidden is clear. The failure is happening on Twilio’s side due to SIP authentication errors. Twilio returns:

X-Twilio-Error: 32202 Authentication failure - bad user credentials

The SIP flow shows Twilio receiving your INVITE and immediately responding with a 403 Forbidden, meaning the request reached Twilio successfully, but the credentials did not match. Here’s what we recommend: 1. Verify your Twilio SIP Credentials - SIP username - SIP password Make sure they’re the current values and weren’t recently rotated. 2. Confirm the SIP Domain The domain in the request resolves to:

[ R E D A C T E D ].sip.twilio.com

Ensure this exact SIP domain is configured correctly in your Twilio console. 3. Regenerate Credentials if Needed If there's any doubt, regenerate your SIP credentials in Twilio and update them in your Vapi SIP trunk settings. 4. Check Twilio SIP Logs Twilio will show more detailed authentication failures under your SIP Domain logs. The good news: This is not a network or firewall issue. Your packets reach Twilio correctly — the issue is strictly an authentication mismatch.