A 5xx error occurs when there is an issue communicating with your origin server.
Error 523: origin is unreachable
Error 523 occurs when Cloudflare cannot contact your origin web server. This typically occurs when a network device between Cloudflare and the origin web server doesn’t have a route to the origin’s IP address.
Error 524: a timeout occurred
Error 524 indicates that Cloudflare successfully connected to the origin web server, but the origin did not provide an HTTP response before the default 100 second connection timed out.