can I test 'fail to fetch url' feed?

I want to make new RSS by using this site.

I made like this. I add this feed in my account, and change proxy server.
but still there are nothing in feed-items.

Can I test this feed?

This particular site appears to be using Cloudflare to protect access to its pages, so it might not be very easy to bypass that without using a conventional browser to access the page.