Subdomain redirectionj doesn't work

[fritex]

Greetings,

Thank you for asking.

Regarding Cloudflare 521 error, may I ask which suggestions from below article for have you tried for further troubleshooting?

Community Tip - Fixing Error 521: Web server is down

Error Try the suggestions in this Community Tip to help you fix Error 521: Web server is down. Background A 521 error happens when we are unable to make a TCP connection to your origin server. Specifically, Cloudflare tried to connect to your origin server on port 80 or 443, but received a connection refused error. This is often caused by security or firewall software and happens if the origin server has directly refused Cloudflare’s proxy request. [Banner in tip catalog] Quick Fix Ideas …

Before moving to Cloudflare, was your sub-domain working over HTTPS connection with a valid SSL certificate?

Is your sub-domain hostname like sub.domain.com or www.sub.domain.com?

Kindly, before doing anything at Cloudflare settings, you could determine if you have a valid SSL certificate installed at the origin host/server by your web hosting provider or your own VPS/dedicated server following the steps from below:

1. Use the “Pause Cloudflare on Site” option from the Overview tab for your domain at dash.cloudflare.com .
2. The link is in the lower right corner of that page.
3. Give it five minutes to take effect, then make sure site is working as expected with HTTPS.
4. Check with your hosting provider / cPanel AutoSSL / ACME.sh / Certbot / Let’s Encrypt or some other and renew it accordingly.
5. Only then should you un-pause Cloudflare and double-check your SSL/TLS setting to make sure it’s Full (Strict).

May I ask what SSL option have you got selected under the SSL/TLS tab at Cloudflare dashboard for your domain ( Flexible, Full, Full Strict … )?

Here is a way to re-check if you correctly setup the SSL for your domain with Cloudflare:

Deprecated - Step 2: Setting up SSL with Cloudflare

This tutorial is deprecated in favour of Get started with SSL/TLS · Cloudflare SSL/TLS docs

Archive

This tutorial covers getting SSL working with Cloudflare in various different scenarios. This assumes you already have your website set up on Cloudflare with all your DNS records set to , if not - please visit <a href="https://community.cloudflare.com/t/64309">Step 1</a>. Do you want the website to use HTTPS? Yes Do you already have a valid SSL certificate installed…

In case you do not have an SSL certificate, you can use Cloudflare SSL, if so, kindly make sure you follow the instructions as follows on the below article to setup an SSL certificate using Cloudflare Origin CA Certificate:

• Origin CA certificates · Cloudflare SSL/TLS docs

Last but not least, kindly have a look here for more information regarding correct SSL settings at the SSL/TLS tab on Cloudflare dashboard:

Why you should choose Full Strict, and only Full Strict

Unencrypted & unverified connections Imagine you open Paypal and suddenly get that warning [image] Would you continue? Probably not. For decades leaders in IT security have advocated that people upgrade their sites from unencrypted HTTP to secure HTTPS. And for a reason, everything you send via an HTTP connection is sent in plain text and can be intercepted at any point between you and the server. Equally, you’d probably not proceed if you got such a warning, right? [image] That’s when th…

Furthermore, do not skip below step and kindly re-check if Cloudflare is allowed to connect to your origin host to as follows in the below article:

• https://support.cloudflare.com/hc/en-us/articles/201897700-Allowing-Cloudflare-IP-addresses

Nevertheless, Cloudflare IP addresses list can be found here:

IP Ranges