This error means that the name on the certificate is not recognized and is usually caused by a SSL configuration error. The first thing to do is to check for any errors in your certificate using the Qualys SSL Labs scan. If there are any issues with your certificate the scan will tell you. Do you see any error messages? Then it’s likely the error is related to your certificate configuration, contact your hosting or certificate provider to help solve this issue.
If the scan returns no errors there might something wrong in your browser configuration. The first thing is to check if you are using the latest version of your browser. After that try clearing the browsers cache. If that doesn’t solve the issue either there are a lot of guides available online to troubleshoot the err_ssl_unrecognized_name_alert when it’s browser related.