Troubleshooting Voice Call connectivity Issues

Symptom

When placing outbound voice calls, the call is not connected or fails with an error. 

Applies To

• Voice API
• SIP Trunking
• Programmable SIP

Common Reasons for Call Failures

• Caller ID issues
  If you set the CLI as a non-Vonage API number or with an invalid CLI, the call will be rejected. When using the Vonage Voice API, Programmable SIP, or SIP trunking, you will need to purchase a virtual number from Vonage and use this as your CLI. For additional information, please refer to: Does the Vonage API Platform support CLI/Caller ID for my voice calls?

  Additionally, calls placed with an in-country CLI when terminating locally are often subject to rejection by destination operators. This is due to regulatory restrictions to protect subscribers from spoofing or malicious traffic. Calls made without a CLI (no-CLI or anonymous calls) are also subject to rejection by the Vonage API Platform. For further details, please refer to: In-Country, Local, or No-CLI Calls Rejected

• Country-Specific Features and Restrictions
  In some cases, call failures can occur due to country-specific limitations. If the feature you're trying to use isn’t available in your location, or if there are regulatory or network restrictions affecting that feature, the call may not connect or function as expected. For more details, please refer to our Country-Specific Features and Restrictions article.

• Call Filtering & Spam Detection
  Carriers often apply spam filtering that may block or drop calls identified as suspicious, such as high-volume traffic, short-duration calls, or text-to-speech (TTS) generated calls. For additional information, please refer to:

      Why does Caller ID show as potential spam?

      STIR/SHAKEN Caller ID Authentication and Robocalls 

• Endpoint/Handset Issues
  The receiving handset may be switched off, out of coverage, forwarded to voicemail, or unable to receive the call. In some cases, the calling number may be blocked by the recipient.

SIP Response Codes

If your call returns any of the SIP error codes, review the possible causes in this KB article.

If you have verified everything on your end for the above errors and confirmed that your setup is not causing the issue, or you receive a 5XX response code (e.g., 500, 503, 504), it’s advisable to contact the Vonage Support team with call details for further investigation.

Additional Information

When a Vonage API user opens a ticket regarding Voice call connectivity issues, our Support team investigates this through multiple troubleshooting steps.

Sometimes, these steps are not enough to identify the exact reason why a call could have failed. In those cases, the next step is to open a ticket with the relevant route provider.

For more details, please refer to: How does Vonage investigate Voice call connectivity issues?