This is HTTPS protocol.

Issue details

HTTPS pages on your website with the canonical link pointing to an HTTP page.

Similar or duplicate pages of your website must have a "rel=canonical" attribute to instruct search engines to show the most authoritative (canonical) version of the page in search results. See recommendations from Google here.

How to fix

HTTPS is one of the ranking signals for Google. Make sure the canonical URLs on your website point to HTTPS pages.

Keep in mind that Google prefers HTTPS pages over equivalent HTTP pages as canonical.