How do I troubleshoot SSL/TLS protocol version issues that might cause a handshake failure between Cloudflare and Nginx?

Check your Nginx configuration for the `ssl_protocols` directive. Ensure it includes `TLSv1.2` and `TLSv1.3` and that older, insecure protocols like SSLv3 and TLSv1.0 are disabled. You can also use the `nmap` command to scan your server and determine which SSL/TLS protocols are supported: `nmap --script ssl-enum-ciphers -p 443 yourdomain.com`. This will help you identify any outdated protocols that need to be disabled.