What it means
The request needs authentication and the server has sent a challenge. This is normal on the first REGISTER or INVITE. Your device should answer with credentials and resend.
SIP/2.0 401 Unauthorized
Common causes
- First request sent without credentials, which is expected behavior
- Wrong username, password, or realm in the response
- Clock skew making the nonce look stale
- The device is not handling the digest challenge and resending
How to fix it
- Resend the request with a valid Authorization header using the correct username, password and realm
- Confirm the credentials match what the provider issued
- Check that your device automatically answers the challenge
- Fix large clock differences that can invalidate the nonce
See it in your own trace
Paste a full SIP or Asterisk log into the decoder and ladder tools to see exactly where this response appears in the call and what led to it. Everything runs in your browser, so your logs never leave your device.
Open the SIP decoder
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