How to resolve a 403 Forbidden Error on a new site?

[abzalali]

Hi, thanks for your time, First of all, it's a new site and no plan activate currently. I'm trying to post the number of product shows per page. My code is as below:

$('#paginateBy').on('change', function(){  
      var val = $(this).val();
	  $.ajax({
      type: "POST",
      url: '/cart.js',
      data: {"attributes[pagination]": val},
      success: function(d){
        window.location.reload();
        },
      dataType: 'json'
      });
});

I'm getting this error:

Any help would be much appreciated.

Thanks in Advance.