Mixed content occurs when elements on a secure page load over an unsecured connection – images, scripts, styles, or embedded videos. The browser will warn about this, or block such elements outright, which breaks the page's layout or stops an interactive part from working. The user sees a warning about an untrusted connection, which for an e-commerce store means an immediate loss of trust. The solution has three steps. Make sure the entire website runs over a secure connection with a valid certificate, and that unsecured URLs redirect permanently. Go through the templates and content and fix the links to elements that load insecurely. And check that the certificate does not expire – monitor its validity automatically, not manually. After switching to a secure connection, also check that the sitemaps, canonical links, and analytics settings point to the new version.
Source: web.dev
See also: HTTP status codes, Trust signals, Canonical domain version.
