Our BYO SIP trunk stops working because Vapi is not maintaining SIP registration. Provider confirms: "Your account is not registered in our system. Registration status must be maintained." Configuration: - Credential ID: 0e846d42-7d85-4484-8ea6-d93dcf10503f - "Use SIP Registration" enabled - Domain: voip.plfon.pl - Username: SLAPProduction Issue: Despite having "Use SIP Registration" enabled, our provider shows we are NOT registered at 08:33. Questions: 1. Does Vapi automatically send REGISTER requests? 2. Does Vapi automatically REFRESH registration before it expires? 3. What is the registration refresh interval? 4. Can you confirm REGISTER requests are being sent to voip.plfon.pl? Per RFC 3261: "Each UA is responsible for refreshing the bindings that it has previously established" Without active registration: - Inbound calls fail - Outbound calls fail with 480 error Please investigate why registration is not being maintained.

Hi Marcello, To help you with any SIP trunk connection errors, please ensure the following: 1. Check Network Requirements: Ensure that the IP addresses

44.229.228.186/32

and

44.238.177.138/32

are allowlisted for SIP traffic [here](https://docs.vapi.ai/advanced/sip/sip-trunk). 2. Authentication Method: For IP-based authentication, confirm your SIP provider offers a unique termination URI or dedicated SIP server. This setup is crucial for proper routing. 3. Error Codes: Update your error handling to utilize specific SIP error codes such as

call.in-progress.error-providerfault-outbound-sip-403-forbidden

and

call.in-progress.error-providerfault-outbound-sip-503-service-unavailable

[here](https://docs.vapi.ai/changelog/2025/5/31). If you encounter specific error codes or issues, feel free to share them, and I can assist further.