Insert an array with PDO

I have a problem trying to insert an array

This is the insert code

public $campos=array("id_transaccion","id_producto","id_empleado","cantidad","id_cliente","fecha");
    public $tabla="ventas";
    public $tablaWeb="transacciones";
public function CompraWeb($datos=array(),$cuenta,$id)
    {
        $arreglo=array();

        foreach ($datos as $key=>$value) 
        {
            if(in_array($key,$this->campos))
            {
                //líena que muestra el arreglo
                $arreglo[$key]=$value; 

            }
        }
        for ($i=0; $i <count($arreglo) ; $i++) { 

        print_r($arreglo);
        $keys=implode(",",array_keys($arreglo));
        $values=implode("','",array_values($arreglo));
        $sql=sprintf("insert into %s (%s)  values('%s')",$this->tablaWeb,$keys,$values);

        if ($this->ValidarCuenta($cuenta,$id) == true) 
        {
                $this->conexion->exec($sql);
                echo '<script language="javascript">alert("Compra Exitosa");</script>'; 
                header("Refresh:0; url=../views/ProductosCliente.php");

        }
        else
        {
            echo '<script language="javascript">alert("Pongase en contacto con el Administrador para que reciba una cuenta");</script>'; 
            header("Refresh:0; url=../views/ProductosCliente.php");
        }
    }
}

This is what I get from the controller

<?php 
session_start();
include_once ("../model/Ventas.php");

$cuenta=$_POST['cuenta'];
$id=$_POST['id_cliente'];

var_dump($_POST);
var_dump($_SESSION['carrito']);
$conexion=new Ventas();
$conexion->CompraWeb($_SESSION['carrito'],$cuenta,$id);

Show me an arrangement this way ...

  

array (6) {["product_name"] = > string (8) "Food" ["customer_id"] = > string (1) "1" ["product_id"] = > string (10) "2017-08-08" ["quantity"] = > string (1) "3" ["image_product"] = > string (33) "../images/alimento_para_perro.jpg" ["product_price"] = > string (2) "15"}

It does not throw me any error, it just gets stuck on the page in the controller and does not do anything