If you get a 521 error and you’re using a custom domain that you’ve set up with Cloudflare, the error is not being reported by ClickMagick, but by Cloudflare. That’s not saying that Cloudflare is doing anything wrong—it’s simply the service that is reporting the error.

To see an explanation of the 521 error that Cloudflare reports, click on this link to read Cloudflare’s knowledge base article:

Troubleshooting Cloudflare 521 errors

Article 574 Last updated: 07/29/2020 6:09:58 AM
https://www.clickmagick.com/kb/?article=574