Google Funding Choices Form Won't Load

I'm trying out Google Funding Choices, but I can't even get the base form to load, following Google's instructions to the letter. I've set up the relevant site and its consent details, configured a basic message for Ad Blocking, pasted in the code snippet output from the deployment instructions in the FC console, and I placed the following from Google's FC documentation before the FC tag, just to try getting the form to load, but this isn't working (and I'm using the url params ?fc=alwaysshow&fctype=ab):

  <script>
      // Make sure that the properties exist on the window.
      window.googlefc = window.googlefc || {};
      window.googlefc.callbackQueue = window.googlefc.callbackQueue || [];
  
      // To guarantee functionality, this must go before the FC tag on the page.
      googlefc.controlledMessagingFunction = (message) => {
       user.isSubscriber().then(
         function (isSubscriber) {
           // Do not show the message if a user is a subscriber.
           if (isSubscriber) {
             message.proceed(false);
           } else {
             message.proceed(true);
           }
         }
       )};
    </script>

Thanks in advance for any guidance