The normal way of testing a site with the final domain url set in place is to spoof the DNS record by making a HOSTS file entry. As the public DNS record does not exist, I may add to my host file something like
in order to fake the production server at the IP address 188.8.131.52. This would naturally only work on my on PC but would be just fine to see all settings are correct before going live.
Once doing so, I received the error 1001 from Cloudflare, which stated that there was something wrong in the configuration.
I think the reason that this does not work is (uneducated answer warning) that Cloudflare makes a ‘reverse’ DNS lookup to confirm the target DNS record. And in the HOSTS file solution (as in internal DNS server configurations as well) this fails.
Too bad, this was such an easy way to test.