A DNS resolution error typically indicates one of the following things:
- A request for a domain was made to a Cloudflare IP address and that domain does not exist on the Cloudflare network, ie- the domain hasn't been added to a Cloudflare account. As a result, Cloudflare does not know where to route that request.
- The target of the DNS record for the domain requested through Cloudflare does not resolve.
- The record requested is a CNAME record pointing to an external DNS provider that is currently experiencing downtime.
Note that this isn't he actual HTTP status code returned for this error: you'll instead see a 409 Conflict if viewing this via cURL/browser network diagnostic tools.