From when I setup my Railgun, I asked CF support about the test button, they said it’s only testing against top level domain and to ignore test button results if you setup Railgun on a subdomain like you have. So don’t use test button to gauge if Railgun is working for subdomain setups. However, your subdomain isn’t matching http://railgun.supportedns.com/ vs http://learn-greek-online.com/ ??
If you’re on Cloudflare Business plan, contact tech support. If you are using Cloudflare Railgun via a CF optimized hosting partner, then they should be the ones properly configuring CF Railgun for you.
I have a shared hosting plan with my webhost. I also have the FREE version of CF. I registered through CF, not through the webhost.
As far as I can see, there is nothing to setup for Railgun, either in the CF control panel, or on my webhost cpanel. My host and CF, they both said it is an issue that they have to solve. They had said this a year ago and it is still not solved.