Hello Support Team, I am experiencing a persistent issue where my Vapi number, sourced from Zadarma, receives inbound calls successfully, but all outbound calls fail. I have performed extensive troubleshooting and require assistance checking the SIP logs, as the problem appears to be a final rejection from the Zadarma side. Here are the details of my setup and troubleshooting steps: Credential ID (The one that fails): aa20fed9-32c6-4b3b-898d-b3fef49c83a3 Credential Name: Zadarma-NoPlus SIP Account Type: Main Zadarma SIP Account (PBX has been disabled). Authentication Used: Main SIP Login (850561) @ sip.zadarma.com. Troubleshooting Status: Authentication Fixed: The Vapi Private Key is confirmed to be working. Trunk Creation Fixed: The SIP Trunk Credential (aa20fed9-32c6-4b3b-898d-b3fef49c83a3) was successfully created and is linked to the phone number. Number Format Tested: I have tested two versions (outboundLeadingPlusEnabled: true and false). The current linked version is false. Request for Logs: Please review the SIP logs for the most recent failed outbound call attempt from my number using the Credential ID aa20fed9-32c6-4b3b-898d-b3fef49c83a3. We need the exact SIP rejection code that Zadarma is sending back (e.g., 403 Forbidden, 603 Declined). This is the last piece of information required to complete the fix. Thank you for your help!

Hi there, I can help analyze your SIP logs and pinpoint why Zadarma is rejecting your outbound calls, including identifying the exact SIP response code. Often, issues like this stem from number formatting, authentication mismatches, or trunk settings, so reviewing the logs will give us a clear answer. To narrow it down faster, could you confirm if all outbound calls fail or only calls to certain destinations? @Daniel

All of them fail

Thanks for confirming all outbound calls fail — that helps a lot. It sounds like an authentication or trunk setup issue between Vapi and Zadarma. I can help check your SIP flow and fix the rejection problem. Once I review the setup, we can get your outbound calls working again. Let’s connect and to help you sort it out . @Daniel

@Vignxt Flow Thanks so much for offering to help! I'm ready when you are. Here is the key information for the logs: - Credential ID:

aa20fed9-32c6-4b3b-898d-b3fef49c83a3

- Last Failed Call: I just attempted another one within the last 5-10 minutes (around 12:50 PM EEST, Oct 15th). Let me know what you need from me to check the SIP logs. Thank you!

You wont get any help here

Hi Daniel, If you're encountering issues with outbound calls, here are some steps you might find helpful to troubleshoot and resolve the problem: 1. **Verify Configuration**: - Ensure your call setup in Vapi is properly configured with a valid assistant, phone number, and customer destination. Review the JSON structure in the outbound calling setup [here](https://docs.vapi.ai/outbound-calling#outbound-calls). 2. **Check Ended Reason**: - Review the call logs for the

endedReason

field. You can find a list of possible ended reasons and what they mean [here](https://docs.vapi.ai/calls/call-ended-reason). 3. **Troubleshoot Call Drop**: - If calls are dropping, especially during transfer, see the steps [here](https://docs.vapi.ai/phone-calling/transfer-calls/debug-forwarding-drops) to debug call forwarding issues. Ensure Vapi initiated the forwarding successfully, and check your telephony provider for logs if needed. 4. **Outbound Campaigns**: - If using outbound campaigns, verify recipient details are correctly formatted in the E.164 standard. Campaign setup guidelines can be found [here](https://docs.vapi.ai/outbound-campaigns/overview). 5. **Caller Identification**: - Implement

STIR/SHAKEN

and

CNAM

registration to enhance call reputation and avoid being flagged as spam. Details on trusted calling practices are available [here](https://docs.vapi.ai/calls/outbound-calling#trusted-calling-and-caller-id). 6. **Provider Logs**: - Check your telephony provider (e.g., Twilio) logs for any specific errors using the

phoneCallProviderId

to search. 7. **Concurrency Limits**: - Ensure your call concurrency limits are not exceeded. For more on managing concurrency in calls, look [here](https://docs.vapi.ai/outbound-campaigns/overview#concurrency). If you've followed these steps and still encounter issues, the problem might lie within the specific configurations or technical setup outside of Vapi's control.