Inbound SIP trunk issue (Czech provider IPEX → VAPI) – call not reaching VAPI
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
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 descriptionWhen 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 IPEX2025-09-17 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 questionsWhy 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
