Error 521 - Cloudfare and NPM


My domain name:
For some reason my domain name and subdomains always gives me Error 521, I have an Origin certificate and website itself is encrypted through letsencrypt/nginx proxy manager.

On letsdebug the server seems fine and keycdn looks fine as well but always get an Error 521. I understand this might be a server issue but my ip address accessibility is working find and server and its services are accessible through SSH and Web UI.

I have a running system on Pi 4 with Debian and following softwares OMV, NextCloud, Nginx proxy manager, Portainer, Jellyfin, Cloudflare DDNS.

Cloudflare certificate is on the Origin Server → SSL set to Full → linked in NPM and subdomain is encrypted with Let’s Encrypt (keeping in mind MX records are set up to public ip for www & domain name)

Please guide me where would be the issue as I am not an expert and I am just setting this up for my home and want to access the services from outside my home network safely.

You should set it to Full (Strict) for additional security! Below is an article on why you should set Full (Strict)

I actually have done all the above nothing fixed this @user22868 and switched Full Strick nothing.

So the problem isn’t resolved?

In that case, email [email protected], then post the ticket number here so we can escalate the ticket for you!


Thank you for writing.

I am sorry to hear you are experiencing an issue.

May I ask is Cloudflare allowed to connect to your RPi? (iptables, firewall …)

May I ask is the Web UI working over a supported and compatible port?

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