Hello, When attempting outbound calls through our SIP Trunk, approximately 33% of the calls fail with the following error message: "call.in-progress.error-providerfault-outbound-sip-480-temporarily-unavailable" In these cases, the call does not start at all. Here are some sample Call IDs for reference: - c563c573-bd6f-44cc-9e6b-5bcdbbc95283 - d244e663-7efb-4001-a76b-3a6d5a3f8342 - 5189bfd8-b77b-4db8-8b66-bff2deb1cd0b Could you please help us identify the exact cause of this error and advise on how we can resolve it? Thank you for your support.

Suggestion: Please verify that you have allowlisted the following Vapi signaling IP addresses in your SIP provider's firewall or access control list, as missing this step can cause outbound call failures:

44.229.228.186/32
44.238.177.138/32

After updating, test outbound calls again to see if the error persists. [See Vapi SIP Trunk Network Requirements](https://docs.vapi.ai/advanced/sip/sip-trunk#network-requirements) Source: - [Vapi SIP Trunk Network Requirements](https://docs.vapi.ai/advanced/sip/sip-trunk#network-requirements)

Thank you for your suggestion. I would like to clarify that we are not seeing this error on every outbound call. The majority of calls are successful, but we intermittently receive the error call.in-progress.error-providerfault-outbound-sip-480-temporarily-unavailable. Could you please explain what might cause this issue to occur only sometimes rather than consistently?

@Yavuz Kömeçoğlu A SIP 480 Error means: I tried calling the remote destination, but no one picked up and all applicable timers (both SIP and application level timers) had expired, thus, the call actively timed-out, because there was no answer at the remote side

Thank you for the information. When we retested the same, yes, it gives this error message when we don't receive a response for a long time. We'll consider it a missed call. Thank you.

Hello, Sorry for the inconvenience and thanks for your patience. Don’t hesitate to contact us again let us know if you need further assistance.