The "Unable to Establish Secure Connection" error in WordPress typically occurs when there is an issue with the SSL certificate or the configuration of your server. Here are steps you can take to troubleshoot and resolve this issue:

1. Check SSL Certificate:

   • Ensure that your SSL certificate is valid and hasn't expired.
   • Verify that the certificate is installed correctly on your server.

2. Check SSL Configuration:

   • Ensure that SSL is properly configured on your web server. This might involve checking your web server's configuration files (e.g., Apache's httpd.conf, Nginx's nginx.conf), and making sure that SSL is enabled and configured correctly.

3. Check Server Date and Time:

   • Make sure the date and time on your server are set correctly. SSL certificates are time-sensitive, and if your server's time is significantly off, it may cause SSL errors.

4. Mixed Content:

   • Check for mixed content issues. This happens when your website loads resources (like images, scripts, or stylesheets) over HTTP instead of HTTPS. This can be fixed by updating the resource links to use HTTPS.

5. Check for Plugin or Theme Conflicts:

   • Sometimes, a faulty plugin or theme might be causing the issue. Try disabling all plugins and switching to a default WordPress theme (like Twenty Twenty-One) to see if the error persists.

6. Update WordPress and Plugins:

   • Ensure that both WordPress and all plugins are updated to the latest versions. Outdated software can sometimes lead to compatibility issues.

7. Check Server Logs:

   • Review your server's error logs. They might provide more specific information about the cause of the SSL connection issue.

8. Firewall or Security Plugin:

   • If you have a security plugin or firewall in place, it might be overly strict and cause issues. Try temporarily disabling it to see if that resolves the problem.

9. Contact Hosting Provider:

   • If you've tried all the above steps and still can't resolve the issue, it's a good idea to contact your hosting provider. They might be able to provide specific guidance based on their server setup.

10. Check SSL/TLS Protocols:

    • Ensure that your server supports the latest versions of SSL/TLS protocols. Older versions might have security vulnerabilities and could cause connection errors.

11. Check Domain Configuration:

    • Ensure that your domain's DNS settings are correct and pointing to the right server.

Remember to always back up your website before making any significant changes to avoid potential data loss.

If none of these steps work, consider seeking help from a developer or a professional familiar with WordPress and server configurations. They can provide more specific guidance based on the details of your setup.