Block Page on pfSense

I cannot seem to get the block page to load.  All I see is an error in the browser that states "server IP address could not be found."  This behavior occurs across multiple web browsers and all devices in my network.  I followed the steps in the setup guide and pasted the config into the Services -> DNS Resolver page.  Logs and everything are working in my NextDNS account, and clearly pages are being blocked, but the block page does not load despite having it enabled.