Easy FancyBox getElementById

JavaScript

function unsplitCookie() {
  var default_roiz = getCookie("__roiz");

    if (default_roiz != null && default_roiz != "undefined") {
        document.getElementById("formROIVisitor").value = default_roiz;
        //alert(default_roiz); alert works but nothing populates in the value of the input
    }

}

jQuery(document).ready(function(){
  jQuery('form.mkto').submit(function(){
    unsplitCookie();
  });
});

HTML of Form inside fancybox
<div style=”display:none” class=”fancybox-hidden”>
<div id=”fancyboxID-1″>`
<form class=”mkto” action=””>
<input type=”text” name=”formROIVisitor” id=”formROIVisitor” value=”” />
<button type=”submit”>Submit</button>
</form>
</div>
</div>

<a href=”#fancyboxID-1″ class=”fancybox-inline”>Request a Info Kit.</a>`

I get a JavaScript error using FF.
Error: TypeError: document.getElementById(…) is null
Source File: chrome://web-developer/content/overlay/javascript/overlay.js
Line: 7333

When I pull the form outside of the fancy box everything works as expected. Not sure why the document.getElementById is not passing. Any suggestions would be great!

https://www.ads-software.com/plugins/easy-fancybox/