This KB Helps you how to fix the connection not secure error on your domain (How to install Free SSL Letencrypt over AutoSSL) 

Login to your cPanel > SSL/TLS Status  > Run AutoSSL

It will install the Free SSL from Letsencrypt.

Please allow some time as it need to verify your DNS and other settings before the installation

Make sure your domain has been pointed to our Server IP/Nameservers/DNS so it will install the SSL.

or 

* Login to cPanel and you can find icon "Letsencrypt" under security Section 
* Click on the Letsencrypt icon 
* Click on the Button "New SSL Certificate" An Pop Box will be open and select your domain in which you need to install the SSL. Once you select the domain you'll see an another option with "Select Alt-Domains" In that Select all the alias in which the SSL Will be installed.


If you didn't select the alt-domains you will get Error at the time of installation and SSL Will not be installed So please select the Alt-Domains and Click submit.