HTML - nesesito ayuda porfavor

<form name='formTpv' method='post' action='https://www.sandbox.paypal.com/cgi-bin/webscr' style="border: 1px solid #CECECE;padding-left: 10px;">

    <input name="cmd" type="hidden" value="_cart">

    <input name="upload" type="hidden" value="1">

    <input name="business" type="hidden" value="vender@hotmail.com">

    <input name="shopping_url" type="hidden" value="http://localhost/mitienda/productos.php">

    <input name="currency_code" type="hidden" value="EUR">

    <input name="return" type="hidden" value="http://localhost/mi_carrito/exito.php">

    <input type='hidden' name='cancel_return' value='http://localhost/mi_carrito/errorPaypal.php'>

    <input name="notify_url" type="hidden" value="http://localhost/mi_carrito/paypalipn.php">

    <input name="rm" type="hidden" value="2">

    <?php

        $contador = 0;

        foreach($_SESSION['carro'] as $key=>$valor){

                $contador ++;

                $fi=$obj->getProductosPorId($key);

                foreach($fi as $fila){

                $id=$fila['id'];

                $producto=$fila['producto'];

                $precio=$fila['precio'];

        }

   ?>

  <input name="item_number_<?php echo $contador; ?>" type="hidden" value="<?php echo $id; ?>">

  <input name="item_name_<?php echo $contador; ?>" type="hidden" value="<?php echo $producto; ?>">

  <input name="amount_<?php echo $contador; ?>" type="hidden" value="<?php echo $precio; ?>">

  <input name="quantity_<?php echo $contador; ?>" type="hidden" value="<?php echo $valor; ?>">

  <?php

      }

  ?>

  <input type="submit" value="PayPal SandBox">-

</form>