HTTPS URL links to an HTTP URL
This means that the URL in question uses the HTTPS protocol, but contains outgoing links to internal URLs which are on HTTP.
Why is this important?
If a URL is loaded over the HTTPS protocol, this means all communications between the users' browser and the website are encrypted. Linking to internal HTTP pages may be a mistake in the <a href> reference. If not, then serving some pages over HTTP may negatively affect user experience and their confidence in your website.
What does the Hint check?
This Hint will trigger for any internal HTTPS URL which includes links to any HTTP URL (internal links only).
Examples that trigger this Hint:
Consider the URL: https://example.com/page-a
The Hint would trigger for this URL if it contained even a single <a href> link to an internal HTTP URL:
Why is this Hint marked 'Advisory'?
While it is recommended for all webpages to be served over HTTPS, it is still acceptable to have a website using HTTPS for some pages and HTTP for others.
The best approach would be to load the entire site over HTTPS, since there are loads of good reasons to do this.
If the entire site already loads of HTTPS, then you can resolve this issue easily by updating the <a href> reference(s) to point to the HTTPS version.