This page has javascript header injection that catches on load the URL parameters provided to the page, identifies the hidden parameter "SOURCE" and updates the value automatically to be set from the URL parameter utm_source.

This offers the means to automatically extract additional URL parameters that are not named correctly (SQF_SOURCE) for the squarespace framework to automatically extract, and have them pushed into the hidden fields on the form.

The javascript is as follows

<script type="text/javascript">

   function querySt(param) {
     p = window.location.search.substring(1); 
     ps = p.split("&"); 
     for (i=0;i<ps.length;i++) { 
       pair = ps[i].split("="); 
       if (pair[0] == param) { 
         return pair[1]; 
       } 
     } 
   }

   Y.on('domready', function() {
       var UTM_SRC= querySt('utm_source');
       var hUtmSrc=Y.all('input[name="SQF_SOURCE"]');
       hUtmSrc.setAttribute('value', UTM_SRC);
   });
  
</script>