Issue
Outbound call failures can be frustrating, especially when a call attempt results in a 603 Decline error. This article explains what a 603 Decline means, why it occurs, and the steps you can take to resolve it.
What is a 603 Decline Error?
603 Decline is a standard SIP response code that indicates the call was actively rejected somewhere in the route — by the recipient, the recipient's carrier, or an intermediate carrier. It is not a Twilio-specific error. Common causes include the recipient not accepting calls or a carrier declining them outright.
Product
Programmable Voice & Elastic SIP Trunking
Cause
- Carrier Blocking: The recipient’s carrier may be blocking calls from your number.
- Number Reputation: If your Twilio number has been flagged for spam or unwanted calls, carriers may automatically reject calls.
- Recipient Preferences: The called party may have enabled features to block certain calls.
Resolution
-
Identify the Affected Number(s):
Determine which Twilio number(s) are experiencing the issue and which destination numbers are being called. -
Check Call Logs:
Review your Twilio Console’s Voice > Calls logs for the affected calls. Look for the SIP response code and any additional error details. -
Test with Other Numbers:
Try making outbound calls from a different Twilio number or to a different destination to see if the issue is isolated. -
Review Recent Changes:
Consider any recent changes to your Twilio configuration, caller ID, or network environment that might impact call routing. -
Is the Recipient reachable outside from Twilio :
If yes, Issue may lie with Twilio's carrier, intermediate carrier or destination carrier. -
Escalate to Twilio Support:
Gather the following information before reaching out for help:- The affected Twilio number(s)
- The destination number(s)
- Date and time of recent failed calls (in UTC)
- Call SIDs from your Twilio Console
- Any observed error messages or call behavior
- If calls to +1 destinations return a 603, create a Voice Integrity bundle and associate the affected numbers to reduce spam filtering and improve answer rates.
Additional Information
What Twilio Support Will Do
When you contact Twilio Support, our team will:
- Review your call logs and configuration
- Check for any known carrier issues
- Escalate the issue to the carrier if necessary (as in the example ticket, where a carrier escalation was required)
- Keep you updated as we work with the carrier to resolve the problem
Below you will find references to useful documents:
Tip: Always keep your account contact information up to date to ensure you receive important communications from Twilio Support./