AMP Page URL is Not Found (4XX)
This means that the URL in question defines an AMP Page URL that is Not Found (4XX).
Why is this important?
If an AMP Page URL is Not Found (404), search engines will be unable to crawl the page and access the content, which means it will not get indexed or appear in search results.
What does the Hint check?
This Hint will trigger for any internal URL which references an AMP Page, where the AMP page URL returns a 404 HTTP header response.
Examples that trigger this Hint
Consider the URL: https://example.com/page-a/
The Hint would trigger for this URL if it included a <link> tag that referenced an AMP page:
where this AMP page had a 404 (Not Found) header response:
How do you resolve this issue?
AMP URLs need to be accessible in order to be indexed. In this case, either the page is missing/removed, or the <link> tag is pointing to the wrong URL.
To rectify, you would need to ensure that the <link> tag is pointing to the correct (i.e. equivalent) AMP page, and ensure that this page is fully accessible to search engines and users alike, returning a 200 HTTP response.