Hello, my name is Milan Roušavý, I am from the Czech Republic. I am integrating your platform (VAPI) with a SIP trunk from IPEX, which is a Czech VoIP/SIP provider offering DID numbers in the Czech Republic. My provider (IPEX) assigned me the DID number: +420 910 107 712 In VAPI I created an inbound phone number 910107712 (non-E164) and attached it to my assistant. The SIP trunk is configured as static, so I connect only by IP address – no registration is used. On the IPEX side the trunk status shows as Reachable. For IP access, I followed your documentation and whitelisted these signaling IPs in IPEX: 44.229.228.186/32 44.238.177.138/32 📋 Problem description When I call my DID from an external mobile number, IPEX log shows that the call is routed to the trunk muj_demo and the number 910107712. However, the call never appears in VAPI call logs – there is no trace of the inbound INVITE in VAPI. The caller only hears a busy tone. 📑 Log excerpt from IPEX 2025-09-17 22:58:49:498 Volající číslo: 773985625 Volané číslo: 910107712 Vstupní směrování VoIPEX vyhledávací vzor: 910107712 Volám přesměrování na Trunk - muj_demo 2025-09-17 22:58:49:507 Příchozí hovor z čísla 773985625 byl ukončen ❓ My questions Why is the inbound call not visible at all in VAPI call logs, even though IPEX confirms it forwarded the INVITE to the trunk? Does VAPI use any additional signaling IP addresses or subnets that must also be whitelisted on the provider side (IPEX)? Can you provide the complete list of SIP signaling IPs and RTP/media IPs that must be allowed for inbound calls to work? For a static SIP trunk (IP-based only, no registration), is it sufficient to configure only the provider’s IP (212.71.129.36, sip.ipex.cz) on the VAPI side, or should we also configure domain/realm values? Could the issue be related to the number format (E.164 +420910107712 vs. national 910107712) or codec negotiation? Thank you very much for your support and guidance. Best regards, Milan

Suggestion: Please double-check that you have allowlisted both of Vapi's SIP signaling IPs on your IPEX trunk:

44.229.228.186/32
44.238.177.138/32

Missing either IP can prevent inbound calls from reaching Vapi. No additional signaling IPs are documented as required for SIP trunking—ensure these two are fully allowed for both SIP signaling and media traffic on your provider's firewall or access list. [See Vapi SIP trunking docs](https://docs.vapi.ai/advanced/sip/sip-trunk#network-requirements) Source: - [SIP Trunking | Vapi Documentation](https://docs.vapi.ai/advanced/sip/sip-trunk#network-requirements)

problem solved... firewall... thank you