If your browser is showing an "insecure" or "not secured" or similar alert on your site, you need to enable SSL / TLS certificates so that https:// can be used to resolve that error / alert. Please see our other knowledgebase articles on how to do this.
If you have already configured https to be used and still receive an error, ensure that all content on the page is being served from https. This includes images, CSS (style sheets), and javscript (js) files. If those files are served with http:// and not https during a https session, you will see either an error or an alert (depending on browser) indicating that there are mixed content. The easiest method to check this is via the browser's page information window -> media and looking through the list of media to find the item being served with http:// . That window varies among the browsers and some may not offer that also.
Firefox media: right click page and go to "View Page Info" and click the Media tab.
Chrome: right click page and go to "Inspect" and go to Network tab and reload the current page . A list of files will appear with their complete address. Review that list for files not using https in their address.
Edge: options menu (three dots on top right) -> Developer tools -> Network tab and review list of files and their complete URL for any using http:// .