Getting a 521 Error - What's Causing It and How Do I Fix It? or Why Am I Seeing a 521 Error and How C

This error drove me nuts!

For me, it was a misconfigured NGINX listen directive. Cloudflare was hitting port 80, but my server was only listening on 443.

Check your server blocks:

`sudo nginx -T`

Make sure it’s listening on the right ports.