Hi, I have an issue with my SIP trunk integration. Call made from a landline is working fine, however call made from a mobile phone is not delivered to VAPI, I'm receiving a SIP 401 unauthorized. Is there any specific configuration on VAPI side that would gave be SIP 401 challenge for mobile phone initiated calls ONLY? Thanks

Thank you for the details. To help narrow down the cause of the SIP 401 error, could you confirm if both Vapi signaling IPs (

44.229.228.186

and

44.238.177.138

) are allowlisted with your SIP provider for inbound calls? This is a common cause of unauthorized errors according to the documentation I have found ([Vapi SIP trunking guide](https://docs.vapi.ai/advanced/sip/sip-trunk)). Source: - [Vapi SIP trunking guide](https://docs.vapi.ai/advanced/sip/sip-trunk)

Yes both IP are whitelisted. Again, call initiated from landline work fine, only call initiated from mobile phone we received SIP 401.

Vapi does not have any restrictions on mobile vs landline calls. The 401 Unauthorized response is standard SIP digest authentication, it happens for all inbound calls regardless of origin.  The difference you're seeing is likely due to how your SIP provider routes mobile calls. Please:  1. Contact your SIP provider and ask if mobile calls are routed differently  2. Request SIP PCAP traces for both a working (landline) and failing (mobile) call  3. Share those traces with us so we can identify the exact difference  If your provider cannot respond to digest auth challenges for mobile calls, we can whitelist their source IPs on our side. Do share you org id/call id if the issue is not resolved.