Issue
Outgoing calls to external numbers are failing, with the last SIP response code being 603.
Product
Programmable Voice and Elastic SIP Trunking
Cause
A SIP response code 603 from carrier partners generally means that the call was either declined by the recipient or blocked by the carrier due to being flagged as 'Scam Likely', 'Spam', 'Fraud Risk', or 'Robo Call'. This often results in dropped calls and can be frustrating for users. If the called party is actively rejecting the call on their end, unfortunately, this is outside of our control.
Resolution
To help address this issue, we recommend associating your phone numbers with Voice Integrity and other Trust Hub products such as CNAM and SHAKEN/STIR. These measures can reduce the likelihood of inaccurate spam or scam labels and may improve your call answer rates. However, please note that using Voice Integrity, CNAM, and SHAKEN/STIR does not guarantee complete removal of spam labels or prevent call rejections. If a carrier receives reports or complaints of spam, fraud, or robocalls, even for numbers associated with Trust Hub products, they may still block these calls or retain the spam label. Maintaining a positive calling reputation is essential for improving answer rates and minimizing spam labelling.
Additional Information
Outbound Calls Blocked or Labeled as Spam or Scam Likely
Best Practices for Voice Calls Trusted Communication