Really Simple SSL is not an SSL certificate itself but a tool to configure your site for SSL. The plugin requires a valid SSL certificate before it can work correctly. We recommend to contact your hosting provider about this, they have access to the server and can install a valid SSL certificate for you. Alternatively, you can use a solution like SSL Zen: https://really-simple-ssl.com/knowledge-base/installing-an-ssl-certificate/
Once installed, we can help you to configure your site for SSL.
I am keep getting Invalid response ERR_SSL_PROTOCAL_ERROR, tried all possible way but not able to fix it. is there any issue on my certificate or i am missing something. I am completely new on this field.