Hello,
https://support.cloudflare.com/hc/en-us/articles/115003014512-4xx-Client-Error#:~:text=If%20you're%20seeing%20a,permission%20rules%20on%20your%20server.&text=You%20should%20make%20sure%20that%20Cloudflare's%20IPs%20aren't%20being%20blocked.