Cloudflare load balancer 521 error but my server is ok

[MarkMeyer]

Most common reason ist that Cloudflare IPs are blocked or HTTPS is not alowed / configured.

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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 …