To solve this, we need to make sure our installation of SSL is correct. Please check your current website via https://cryptoreport.rapidssl.com/checker/views/certCheck.jsp.
It will show you the missing SSL Certificate. Please download it into your server. The next step will be:
1. go to /etc/ssl
2. move your current domain.crt into another file
3. then concatenate your existing domain.crt (renamed) with intermediate key into new domain.crt
cat existing-domain.crt intermediate.pem > domain.crt
Please double check again with SSL certification checker