Hello, can someone maybe help me out? I’ve got this problem: when there’s an incoming call to the assistant, the transfer call function works perfectly. But when the assistant makes an outbound call, after the agent triggers the transfer call function and delivers the transfer message, the call just ends on the user’s side and the transfer never reaches our target number. What could be the issue? I’m using Telnyx for SIP. https://cdn.discordapp.com/attachments/1421443068757938257/1421443069084958840/telegram-cloud-photo-size-2-5382024695894899288-y.jpg?ex=68d90d84&is=68d7bc04&hm=c652955d29360133db1c3986cdd586e0e66a3f7afb569518cf250507c08fb001&

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Suggestion: Check your assistant's configuration to ensure Vapi is managing call transfers. Set

phoneCallProviderBypassEnabled

to

false

and remove

"phone-call-control"

from

serverMessages

. Here’s an example configuration:

json
{
  "phoneCallProviderBypassEnabled": false,
  "serverMessages": ["conversation-update"]
}

Apply this and test your outbound transfer again—this resolves most SIP transfer drop issues with Telnyx. For more details, see the [Vapi troubleshooting guide](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops#verify-server-message-configuration). Source: - [Debug call forwarding drops](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops)

Hi, I've tried all the troubleshooting steps you provided: ✅ Checked endedReason in call logs - shows "assistant-forwarded-call" (Vapi initiated transfer correctly) ✅ Removed "phone-call-control" from serverMessages ✅ Set phoneCallProviderBypassEnabled: false at call level ✅ Verified destination number format with country code ✅ Tested calling destination directly - works fine ✅ Confirmed transfer scenario is Phone to phone (supported) The issue persists - all outbound transfers still drop immediately after transfer attempt. Through PCAP analysis, I found the root cause: Vapi SBC (44.238.177.138) responds with 503 Service Unavailable to SIP REFER requests from Telnyx. This appears to be a systemic issue with Vapi+Telnyx SIP REFER integration for outbound calls. Dynamic Transfer works fine (uses webhooks), but standard transfer fails consistently. Is this a known limitation of the Vapi+Telnyx integration? Any ETA on SIP REFER support fix?

Is this for web calls or phone call? Please provide a call id for the scenario you described

CLI (caller): +18886751162 CLD (called): +16052046903 Date+Time (UTC): 2025-09-27T15:14:52.977Z SIP Call-ID: 8dd620aa-1657-123f-ddbc-06ee5e4370fb Transfer details: destination +18885792782, mode blind-transfer, sipVerb: refer

I'm having the same issue

any update ?

We apologize for the delay in responses lately. We are in process of making some changes to our workflow in how we handle support requests. The good news is that we are starting to get back on track of having a 48 hour response time and we would like to start cleaning up anything old. With that being said, just wanted to check in with you to see if you have made any progress or changes to your project since support has last reached out.