Confirm what the tool actually retrieved
Inspect the fetched page's title and returned content rather than relying on the URL or a search result snippet. If the content is a sign-in page, the tool has not read the protected article. A browser session may have cookies or permissions that are not part of the agent's fetch request, so your personal access does not imply the tool has the same access.
Check that the URL is the specific article rather than a general landing page, and see whether the publisher offers a public version or documentation page. If the page is private or requires an account, respect that access boundary rather than trying to bypass it through the tool.
Continue with accessible evidence
Look for an official public source or another source that covers the same claim. Compare publication dates and scope, and tell the agent which evidence matters. If you are authorized to use the material, you can supply a relevant excerpt directly, subject to your organization's sharing rules and the content's confidentiality.
Ask the agent to state that the original page could not be retrieved and to distinguish any substitute source from it. This keeps the answer's evidence trail honest. Do not let a sign-in screen or search snippet be summarized as though it contained the protected article's details.