Dear experts, why do I keep getting 520 and 521 errors after configuring CF?
There is an issue with the SSL certificate configuration, please check the SSL certificate configuration.
The server’s website does not have a certificate deployed, because it is simply impossible to apply for one at all!
This is the cf node that your browser cannot connect to.
Even if I turn off CF and only use resolution, I still get an error. Could this be a problem with my server’s IP address?
Ping to check if the resolution has taken effect. If it does, the problem lies with the original site.
ping works fine, there are no issues. Could this be an environment problem? This is a new environment.
Issues such as whether the firewall allows traffic through and whether the web server is running
There is a firewall, but there are no logs stored in it at all. I do not know how to configure this firewall, it is too complicated for me to understand.
Furthermore, everything works normally when I do not use CF, and it works fine when I do not use CF’s DNS resolution. This should not be a server issue.
That can’t be a problem with cf anyway 
cf only has one configuration setting for SSL. If it is configured correctly, any issues are problems with the origin site.