----------------------------- **While I generate an answer, here are some sources that might be helpful**: * [Call Ended Reason]() * [List Calls]() * [Create Phone Call]() * [Get Call]() -----------------------------

### Answer It seems you're encountering a few issues with starting calls on Vapi, specifically with abrupt terminations described as "unknown errors" and hitting concurrency limits. Here are some steps and considerations that might help resolve these issues: 1. **Unknown Error**: The "unknown error" during calls can be particularly challenging as it does not provide specific information about what went wrong. I recommend checking the server-side logs for any additional error messages or unusual activity around the time the errors occurred. 2. **Concurrency Limit Error**: This error typically indicates that multiple call attempts are being made simultaneously beyond the limit allowed by your current Vapi plan or system setup. Ensure that any retries or parallel call setups are managed to stay within the concurrency limits. Adjusting the retry logic and ensuring proper call teardown can help manage this limit more effectively. 3. **Debugging Steps**: - Review the implementation of the call setup in your code to ensure that it aligns with Vapi’s best practices, particularly around error handling and concurrency management. - Test the call flow with minimal setup to isolate whether the issue is with specific configurations or broader system-level problems. 4. **Consult Documentation and Support**: - Ensure that your system’s implementation aligns with the guidelines and configurations suggested in the Vapi documentation. You might find sections like error handling, call setup, and concurrency management particularly useful. - If the problem persists and you're unable to identify the cause from logs and system checks, I recommend reaching out to Vapi support with detailed information including the call IDs, error messages, and descriptions of the steps already taken to troubleshoot the issue. By methodically checking these areas, you can better iso

late the cause of the issues and apply targeted fixes. If there's any other information or specific logs you can provide, that might also help in diagnosing the problem more accurately.

You can use end-call-report for that purpose