Ajax没有显示倒计时的价值

I have a probem with ajax , If I use the following code only with PHP I show the date correctly.

<h2><span class="clock" data-countdown="{{ $subasta->data_final}}"></span></h2>

However , when I try to use this with ajax I don't show the information about the dates , but the other information load correctly.

<h2><span class='clock' data-countdown='"+response[index].data_final+"'></span></h2>

Which is the problem?

All of the ajax code

success:  function (response) {
                    $(response).each(function(index,value)  {
                        $(".product-image-wrapper2").append("<div class='col-sm-4' style='height:500px;'><div class='nombre'>"+ response[index].nombre + "</div><h2><span class='clock' data-countdown='"+response[index].data_final+"'></span></h2><p>"+response[index].descripcion+"<p>"+ response[index].cant_actual +"<p><a class='pujar btn btn-warning'>Pujar</a>");                                                          
                        $(".product-image-wrapper2").append("</div>");
                    });


                },