A Let's Encrypt certificate is shown as installed for the domain in Plesk, but the domain remains visible as insecure in the browser

Symptoms

• A Let's Encrypt certificate is successfully installed on the domain, but the domain remains visible as not secured in the browser.
• While trying to use a different device or a different browser to open the website, the valid SSL certificate is detected properly.
• Third party SSL checker websites such as this one report the SSL for the domain as installed properly

Cause

The browser you are using has cached outdated SSL information for the affected domain locally and does not try to fetch the updated information.

Resolution

Clear your browser's cache or open the domain via the used browser's incognito (private browsing) mode (this mode does not use the locally stored browser cache).