521 Error

A 521 error is a Cloudflare-specific error code for:

"Server appears to be down."

This occurs when the origin web server refuses connections from Cloudflare. Security solutions at your origin may block legitimate connections from certain Cloudflare IP addresses.

The two most common causes of 521 errors are:


Contact your site administrator or hosting provider to eliminate these common causes:

Source: https://support.cloudflare.com/hc/en-us/articles/115003011431#521error