Hey Support, We are trying to connect VAPI to our PBX system and have it setup as an extension so we can have it handle some calls and run some tests. We have got the whole number and sip trunk setup and outbound calls work perfectly but when trying to call in VAPI returns to out PBX and 500 Server internal Error. Wonder if anyone has this up and running

# Check Network and Firewall Configuration A common cause of SIP 500 errors is network/firewall issues. Ensure your firewall is properly configured to allow SIP traffic by: 1. **Whitelist these IP addresses**:

44.229.228.186
   44.238.177.138

2. Verify your PBX is configured to accept connections from

sip.vapi.ai

(not direct IP addresses) 3. Confirm your system handles SIP REFER messages, which VAPI uses for call transfers Sources: - [Discord message about whitelisting IPs](https://discord.com/channels/1211482211119796234/1339949961491644447) - [Discord message about SIP configuration](https://discord.com/channels/1211482211119796234/1336713212233515089) - [Discord message about using sip.vapi.ai](https://discord.com/channels/1211482211119796234/1329037681908383794)

Check server authentication settings, review call logs, ensure SIP service is operational, and test with a direct SIP connection to isolate the issue.

Authenticaiton and registration are all fine and working. Call logs are pointless as we can see from the PCAP the VAPI server is responding to inbound invites with 500 error.

Send your call IDs and PCAP files