If you encounter a secure connection issue on your website, there are a few possible reasons. Here are the most common ones and how to fix them:
ERR_SSL_PROTOCOL_ERROR - if you see this error, it means that the SSL certificate for your website is not installed yet or is having issues. If the certificate is already installed, check this guide: How to Fix ERR_SSL_PROTOCOL_ERROR
Add https:// to your URL on the browser's address bar. If it loads correctly with a padlock next to the address, then all you need to do is force HTTPS for visitors to get the secured version of your website by default
If your website is accessible through https, but the layout appears incorrect, it's likely due to mixed content issues. You can resolve this by referring to the following guide: What to Do if Your Website Shows a Mixed Content Warning
You can also check this video tutorial: