Test conneciton Success but DNS record and service mode say NO

Have you added your domain to cloudflare?

Tutorial: https://support.cloudflare.com/hc/en-us/articles/201720164-Step-2-Create-a-CloudFlare-account-and-add-a-website

Yes, I am definitely using CloudFlare for the domain. I use it for about 40 websites. This plugin is working fine on the other site I have installed it on.

Interestingly the individual page cache purge for a particular page is working from the plugin.