Hi Support, I have an assistant with an Id of 91380364-c3e2-4de2-a7f2-a3e80c896298 that is having some intermittent issues. Over half of the time when we place a call to this assistant, it isn’t receiving the call. We are using a SIP URI with this assistant. Because the call isn't being answered by the assistant, a call log isn't generated so I can't generate a call log on the Vapi dashboard. On our hosted platform, the call logs indicate that the SIP URI device is refusing to receive the call. We have tried rebuilding the assistant from scratch numerous times, as well as rebuilding the SIP URI several times to root any any possible fluke issues. If you could please take a look at this that would be great. Attached is a call log from our platform. If you need anything else please let us know. Thank you, Jared VSR Cloud Communications Support Engineer 530-889-1500 Main Support X2 jared@vsrusa.com https://cdn.discordapp.com/attachments/1431350912844038174/1431350913104347337/message.txt?ex=68fd18ea&is=68fbc76a&hm=2ffe56bff7bc01a07125405ba7692965ed35f1fcc8a2e7b224585ecfda513094&

Hi Jared, Thanks for the detailed report. The issue seems related to intermittent SIP registration or signaling drops between your endpoint and Vapi. Please confirm if your SIP device stays consistently registered and if NAT/firewall rules allow persistent connections to sip.vapi.ai. I’ll review backend connection logs to trace the exact cause and verify if there’s a routing or timeout mismatch. Once confirmed, we can isolate and stabilize the registration flow. @Jared Johnstun

Hi Jared Johnstun, If you're experiencing issues with call transfers where calls drop immediately after initiating transfer, consider the following steps for troubleshooting: 1. **Verify Forwarding Initiation**: Check if Vapi successfully initiated the call forwarding. Look for the

endedReason

in the call logs. If it's

"assistant-forwarded-call"

, Vapi forwarded the call successfully. 2. **Check Configuration**: Ensure your assistant's

serverMessages

are correctly configured. Remove

"phone-call-control"

if it's included, unless you're implementing custom transfer logic. Set

phoneCallProviderBypassEnabled

to

false

. 3. **Telephony Provider Logs**: Use the

phoneCallProviderId

from the Vapi call object to check your telephony provider logs for transfer-related errors. This can be done in the respective dashboards of your providers like Twilio or Vonage. 4. SIP Analysis (if applicable): Download the

pcap

file and use Wireshark to review SIP signaling. Look for

REFER

packets or error responses in the SIP traffic. 5. **Supported Scenarios**: Ensure your transfer scenario is supported. Web-to-phone and PSTN-to-SIP transfers may not work. Refer to the [debug call forwarding drops guide](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops) for more steps. Adjust configurations and verify your telephony setup if any of these issues persist.

Hello, With Vapi all our assistants don't ever get a positive sip registration, though we have verified functionality on over a dozen assistants. Were you able to verify the backend connection logs? Please advise. Thanks again, Jared

Thank you for providing this information. We’ll be looking into it further to better understand the situation and determine the next steps. Our team will update you as soon as we have more details, and we truly appreciate your patience and cooperation in the meantime.