400 The Plain Http Request Was Sent To Https Port

This error message typically indicates that the plain HTTP request was sent to HTTPS port, suggesting a potential issue with SSL/TLS encryption or certificate validation.

1. Check if your domain name is properly configured and associated with an SSL/TLS certificate. Verify that the certificate has been updated and is valid for all ports (HTTP/HTTPS).
2. Ensure that your web server or application is configured to use the HTTPS port, rather than HTTP. You can check this by examining the server's configuration files or using a tool like `ssmce` or `curl` to verify the requested protocol.
3. Double-check the SSL/TLS certificate chain and ensure it includes all required intermediate certificates. A missing or invalid certificate could cause the plain HTTP request to be redirected to HTTPS, leading to this error message.

It's also possible that an issue with your DNS settings or subdomain configuration is causing the error. You can try verifying your DNS settings using tools like `dig` or `nslookup`, and ensure that all subdomains are correctly configured as CNAME records pointing to your web server.

Common Solutions

• Enable SSL/TLS encryption on your website. This will force the browser to request a secure connection, even if it's not explicitly specified in the URL.
• Use an HTTPS proxy server or tunnel to bypass any issues with the website's configuration.

Please note that this is just a general guide and may require more specific troubleshooting steps depending on your specific situation. For further assistance, refer to Cloudflare's documentation and support resources.

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