无法将工作作为ajax发布到php

Where it's my problem for me the code look's fine

$.post("../Backend/buscarCliente.php",{tipoBusqueda:"'"+$('#sltTipoBusqueda').val()+"'"},respuesta);

the php

<?php  
    //include all DAO files
    header('Content-Type: text/html; charset=utf-8');
    require_once('include_dao.php');
    echo $_POST['tipoBusqueda'];
 ?>

i'm already debugged with charles debugging proxy and send this message, so i think the path it's good

enter image description here

Start out really simple, first just do an echo $_POST['tipoBusqueda'] without the includes and see if that works.