Now if I turn off the Cloudflare by pressing the orange cloud button, I can easily access it.
But if I turn it back on I cannot access the domain. It gives error 522 which supposedly means that the server is down which is not. The SSL setup on the hosting is LetsEncrypt
Sorry, but I have no insight into Hurricane Electric’s configuration.
You really don’t need IPv6 on your server if you’re using Cloudflare. Cloudflare will still route IPv6 visitors through to your IPv4 server. I don’t use IPv6 on my servers just to make things simpler. I still see my visitors’ IPv6 addresses in the server log since I’m restoring Visitor IP addresses from the Cloudflare header.