I am encountering a call in progress error when attempting outbound demo calls. Although 5–10 calls are triggered, they fail to connect. The following error is displayed:

call.in-progress.error-sip-outbound-call-failed-to-connect

Please advise on the possible cause and resolution.

Action Required: Please ensure you have allowlisted the following IP addresses in your SIP provider's settings, as missing this step is a common cause of outbound call failures:

44.229.228.186/32
44.238.177.138/32

After allowlisting, test your outbound calls again. This step is essential for SIP signaling and media to work between Vapi and your provider (according to the documentation I have found: https://docs.vapi.ai/advanced/sip/sip-trunk). Source: - [SIP Trunking Documentation](https://docs.vapi.ai/advanced/sip/sip-trunk)

Hi bikaxh, Please confirm you've allowlisted Vapi's SIP IPs on your provider: 44.229.228.186/32 and 44.238.177.138/32 — see https://docs.vapi.ai/advanced/sip/sip-trunk. If already done, try these steps: 1. Collect one failing call_id and run: • GET https://api.vapi.ai/call/{call_id} with your API key to inspect

endedReason

and

phoneCallProviderId

. 2. If

endedReason

shows a SIP/provider error (e.g.,

call.in-progress.error-sip-outbound-call-failed-to-connect

): • Provide the

phoneCallProviderId

to your SIP provider and ask them to check their call logs for that ID/timestamp. 3. Check concurrency/rate limits: • If many calls started at once, pace them (batch/schedule) to avoid provider-side limits. 4. Verify SIP credential config in Vapi: • Correct gateway domain/IP, outbound auth (username/password) if required, and E.164 formatting for destinations. 5. If using Plivo/Twilio, confirm provider-specific notes: • Plivo requires listed ACLs and may not support SIP REFER; Twilio needs the termination/origination settings plus allowlist.