An APT authentication error is a reason to investigate the named software source. Disabling verification can make the update continue while removing the check that identified the problem. Start by separating the failed repository from the rest of the update output.

Record the source and failure

Keep the exact error text, repository address, release name and time. Remove embedded credentials before sharing the record. Check whether this is an official Ubuntu source or a third-party source previously added for one application.

Compare the configured source with the publisher's current instructions for the installed Ubuntu release. A repository URL, supported release or signing key may have changed, but a guessed substitution is not verification. Use the publisher's known official site to confirm a documented transition and any replacement key fingerprint.

APT authenticates repository metadata against configured trust information. Ubuntu recommends keeping third-party trust tied to the relevant source through Signed-By rather than treating an arbitrary downloaded key as globally trusted. The administrator should inspect that association as part of correcting the source.

Restore a verified update path

Avoid remedies that mark the source trusted without verification, permit unauthenticated packages or allow insecure repositories. These change the protection rather than demonstrate that the repository is authentic. A valid signature also does not establish that an unfamiliar supplier is trustworthy; choosing the supplier remains a separate decision.

If the publisher has retired the source or no longer supports this release, document which installed software depends on it and agree a supported replacement or maintenance path. Simply hiding the error by disabling the source can leave that software outside future updates.

After an authorised correction, refresh the package information and check that the specific repository completes authentication without the original warning. Then review the intended package update normally. Keep the corrected source details with the maintenance record so that a quiet update screen is backed by a known, supported source.

Sources: Ubuntu documentation, Ubuntu documentation.