Criticalcss.com does not work despite it's IP address being whitelisted

I have a site setup to use the Cloudflare CDN and firewall, and I’m looking to make use of the Criticalcss.com service using the plugin addon for Autooptimize called CriticalCSS Powerup (available here: https://wordpress.org/plugins/autoptimize-criticalcss/

I’ve found that unless I unproxy the DNS records and completely pause the Cloudflare service, regardless of the IP addresses being whitelisted, the service does not seem to be able to reach my pages to generate CSS.

I’ve also reached out to the company directly for further guidance, but I suspect this is an additional setting or configuration needed inside of my CF dashboard panel in order to allow their service to bypass the firewall and cache entirely and reach my server directly.

Anyone with previous experience with this service have suggestions?