Many times, you will see HTTPS at the home page. However, when you go to any other page, it will show the page is not secure. Although SSL certificate is installed successfully, you may see this error. This happens due to the presence of mixed content on the web page of your e-commerce site.
Mixed content occurs when initial HTML is loaded over a secure HTTPS connection, but other resources (such as images, videos, stylesheets, scripts) are loaded over an insecure HTTP connection. This is called mixed content because both HTTP and HTTPS content are being loaded to display the same page, and the initial request was secure over HTTPS.
When you are facing this issue on the web page, then you can console check that page and replace the content that is causing the issue. To know more about this issue, visit the helpcenter - https://help.storehippo.com/topic/why-https-not-work-on-the-product-page