After the installation of SSL and forced HTTPS protocol, the mixed content issue can appear on the website. This displays a "Not fully secure" warning next to the domain in the URL bar.
Mixed content means that you are trying to load images or other content with HTTP in their links, to fix this, you would simply need to edit all the links on your page to have HTTPS at the beginning instead.
You can see the list of these links by right-clicking anywhere on your website, selecting the "inspect element" and going to the Console tab. HERE is how you can do it on different browsers.
You can also use this website to identify the content that's causing these issues: whynopadlock.com
Install Really Simple SSL WordPress plugin
- Log in to your WordPress dashboard and click on Plugins > Add New
- Install and activate a plugin named "Really Simple SSL"
- Click on Settings > General
- Change the address of your blog from http:// to https://
Install Search & Replace WordPress plugin
- Once you install the plugin press on Tools and Search&Replace.
- To "Search for" field enter the domain's name with HTTP, for example, http://domain-name.com
- To "Replace with" field enter the domain's name with HTTPS, for example, https://domain-name.com
- Tick Select all the tables, untick Dry Run and press button "Do Search & Replace"
That's all! You are good to go and should have your website displayed as Secure now!