There can be several reasons why SSL/HTTPS is not working on your site.
Domain is Newly Hosted
SSL certificate has probably not been activated yet if the domain name is newly hosted. Newly registered or transferred domain can take up to 24 hours for SSL to work. Please try again on the next day. If it still not working after 24 hours, there may be something went wrong with the activation of your certificate and you need to contact your SSL support team to assist further.
SSL is Not Installed Correctly
The SSL certificate should be installed correctly on the server where your website is hosted. Try reinstall the SSL certificate correctly.
Website URL is Not Configured to HTTPS
Purchasing and installing the SSL certificate does not automatically change your website URL from HTTP to HTTPS. Visitors can still access your site using HTTP. If you want to make sure that your site is only accessed through HTTPS, additional configuration with the redirection must be made. Your site URL with the http must be redirected to the https. Some website application or editor needs configuration with their website URL settings and must use the https, instead of http.
Expired SSL Certificate Error
This error occurs when the site’s SSL certificate expires. According to industry standards, SSL certificates cannot have a lifespan longer than 398 days. That means that every website needs to renew or replace its SSL certificate at least once every two years. Make sure that you have successfully renewed your SSL certificate for your domain name. In rare cases, something goes wrong with the renewal of the SSL certificate for your domain.
Mixed Content Error
Domain Name Mismatch Error
This usually happens when you recently changed the domain name of your website. The existing SSL certificate should be reissued to the new domain name and then should be reinstalled on the web hosting server.
SSL Certificate Not Trusted Error
This error indicates that the SSL certificate is signed or approved by a company that the browser does not trust. That means either the company, known as the certificate authority (CA), is not on the browser’s built-in list of trusted certificate providers or that the certificate was issued by the server itself. Certificates issued by the server are often referred to as self-signed certificates.
SSL Certificate Revoked Error
This error indicates that the CA has canceled or revoked the website’s SSL certificate. This could be because the website acquired the certificate with false credentials (whether by accident or on purpose), the key was compromised, or the wrong key was issued.