The observed URL uses secure HTTPS protocol. However, the referenced canonical URL remains on the unsecure HTTP protocol.
Why is this important?
For optimal security and trust, search engines and digital marketers prefer websites to exclusively utilize HTTPS. An HTTPS URL referring to an HTTP canonical URL could confuse search engines about which version should be indexed and recognized. This scenario is commonly seen following a migration from HTTP to HTTPS, where the canonical tags were not corrected to reflect the change.
What does the Optimization check?
The Optimization is activated when an internal HTTPS URL lists a canonical link to an HTTP URL.
Examples that trigger this Optimization:
Given the URL: https://example.com/page-a
This Optimization is activated if the Canonical URL utilized is HTTP:
Canonical link in the <head> to an HTTP URL
<link rel="canonical" href="http://example.com/page-b" />
OR HTTP Header canonical link to an HTTP URL
HTTP/... 200 OK...Link: <http://example.com/page-b>; rel="canonical"
How do you resolve this issue?
In most instances, this issue stems from incorrect configuration settings — though, occasionally, it could be intentional to point HTTPS URLs back to HTTP.
However, if this is not intentional, correcting the canonical URLs from HTTP to HTTPS should resolve the problem. It is often possible to amend this error across multiple pages simultaneously by adjusting the relevant rules or page templates.