Configuration Verified Phone number correctly linked to credential via credentialId Credential shows as active in GET requests Gateway IP corrected from DNS lookup to actual signaling IP Authentication updated via PATCH request Key Questions Why is Vapi falling back to vapi.sip instead of using the BYO trunk? What triggers this fallback? Is the credential being marked as failed internally? Can you provide SIP-level diagnostics: PCAP or SIP trace of authentication attempt Exact 403 response from provider's server What From/To headers Vapi sends Authentication format used (realm/domain?) How to verify password was saved? GET requests don't show password (expected) Is there a validation endpoint? Inbound routing: What SIP URI should provider route calls to? Any specific headers required beyond inboundEnabled: true? What We Need SIP trace of call ID 019a1645-fe0c-7662-8c8c-53e411457614 Reason for fallback to vapi.sip provider Internal credential status - is it marked as failed? Guidance on resolving 403 authentication issue Expected vs Actual Expected: Calls use BYO SIP trunk at 85.194.242.50:5060 Transport shows byo-sip-trunk Authentication succeeds Call completes Actual: Vapi falls back to own trunk (vapi.sip) 403 Forbidden error Call fails in <1 second Context 15+ working Telnyx BYO numbers in same organization Issue persists 24+ hours despite multiple fixes Provider confirms all settings are correct Request: Please investigate why BYO trunk isn't being used and provide SIP diagnostics to resolve authentication failure.

Thank you for the detailed information. To help pinpoint the issue: Can you confirm if your phone number (+48598220061) is explicitly associated with the BYO SIP trunk credential (Credential ID: e657ad51-28d9-4627-ae5c-6ae4063e7301) in your Vapi dashboard or via the API, as described in the [SIP trunking guide](https://docs.vapi.ai/advanced/sip/sip-trunk)? This association is required for outbound calls to use your BYO SIP trunk instead of the default Vapi trunk. Source: - [SIP Trunking Guide](https://docs.vapi.ai/advanced/sip/sip-trunk)

Yes, the phone number is explicitly associated with the BYO SIP trunk credential (Credential ID: e657ad51-28d9-4627-ae5c-6ae4063e7301) in my Vapi dashboard

"Could you please run these two telnet tests from your side and let me know the results? I'm getting the exact same behavior." telnet 44.238.177.138 5060 (Should CONNECT ✅) telnet 44.229.228.186 5060 (Should FAIL or TIMEOUT ❌) "I need to confirm if the second IP is unreachable for you too, which would indicate a routing issue outside of my local network."

Update - I have managed to configure the outbound calling, all is well, but the inbound does not work now. {"id":"6d3b1b2d-cbc4-4537-a780-50a4117577e0","orgId":"25e97c69-9a46-454f-a28c-1a20f5a08c43","provider":"byo-sip-trunk","createdAt":"2025-10-26T06:54:13.890Z","updatedAt":"2025-10-26T17:12:37.340Z","gateways":[{"ip":"85.194.242.50","inboundEnabled":true},{"ip":"85.194.242.51","inboundEnabled":true},{"ip":"85.194.242.52","inboundEnabled":true},{"ip":"85.194.242.53","inboundEnabled":true},{"ip":"85.194.242.54","inboundEnabled":true},{"ip":"85.194.242.55","inboundEnabled":true},{"ip":"185.190.125.130","inboundEnabled":true},{"ip":"185.190.125.131","inboundEnabled":true},{"ip":"185.190.125.132","inboundEnabled":true}],"name":"plfon-no-port","outboundAuthenticationPlan":{"authUsername":"SLAPProduction"},"outboundLeadingPlusEnabled":true} and the inbound calls still doesn't work. please help me out.