Hi, Jake!
The 521 error code means that the server is down, its firewall is blocking Cloudflare, or there’s an issue with its SSL certificate.
I recommend checking details and more info on this article about 521 errors:
https://community.cloudflare.com/t/community-tip-fixing-error-521-web-server-is-down/42461
If the issue continues or get any other error code after following the steps provided in the article please respond to this same post (share some screenshots with the error also help) in that way we can further help you!