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A carrier set up as a Registration trunk, or a SIP device, fails to register or authenticate.

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Quick checks

  • Are you using a Registration trunk, or did you mean IP trunk (no registration, authenticated by IP instead)?
  • Do Auth username, Auth password, and Auth realm exactly match what your carrier or device provider issued you?

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Cause: wrong trunk type for how your carrier authenticates

How to check: Confirm whether your carrier authenticates by IP address or by username/password. Using IP trunk with a carrier that expects registration (or the reverse) fails immediately. How to fix: Set Trunk type to match — see Connect a SIP carrier.

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Cause: authentication credentials are wrong

How to check: Re-check Auth username, Auth password, and Auth realm character-for-character against what your carrier provided. How to fix: Re-enter them. A password field left blank on an edit keeps the existing stored password — if you’re rotating a credential, you must re-type the new password, not only the username.

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Cause: transport or port mismatch

How to check: Confirm Transport (UDP, TCP, or TLS) and Remote port match your carrier’s requirements exactly — UDP on port 5060 is the default, but not universal. How to fix: Correct the transport or port.

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Cause: IP-based auth expected, but credentials were entered

How to check: If your carrier authenticates by IP allowlisting rather than username/password, leave Auth username and Auth password blank. How to fix: Clear those fields.

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If none of this worked