Nintex Form Error: NF.PeoplePickerAPI is not a constructor

I'm trying to clear a People Picker field when a choice field before it changes. I have looked through the forum and know that I have to use "NF.PeoplePickerAPI" to do this with JS but I get through the error when I use the form in "preview" mode.

This is the code:

NWF$(document).ready(function () {

  NWF.FormFiller.Events.RegisterAfterReady(function () {

});

 NWF$('#'+ARCApproval).change(function() {ARCApprovalChanged();});

});

function ARCApprovalChanged() {

    NWF$('#'+ARC1).val('');

    NWF$('#'+ARC2).val('');

    NWF$('#'+NotARC).find("input:radio[value='Executive Manager(EM)']").attr("checked",false); 

    NWF$('#'+NotARC).find("input:radio[value='ETDR']").attr("checked",false);

    var EM1PP = new NF.PeoplePickerAPI ('#'+EM1);

    EM1PP.clear();

    NWF$('#'+EM2).val('');

    var ETDR1PP = new NF.PeoplePickerAPI ('#'+ETDR1);

    ETDR1PP.clear(); 

    NWF$('#'+ETDR2).val(''); 

    NWF$('#'+ETDR3).val('');

}

This is the error:

 

Any insight would be appreciated.