input[] Feld über Ajax laden

Hallo,
ich habe hier eine Warenkorb für den ich eine Aktualisierung der Anzahl möglich machen will:

PHP-Code:

$("#shopping-cart-results").on('submit', '.form-to-update', function(e) {
        
                          
     var productCode = $('input[name="productCode[]"]').serialize();
                
                
                
    var quantity = $('input[name="quantity[]"]').serialize();

     
                  
            $.ajax({ 
                url: "cart_process.php",
                type: "post", 
                data: JSON.stringify({  
        
                           productCode,
                        
                            quantity 
                             
                             })
                       
                      
                    
            }).done();
            
      $("#shopping-cart-results").html('<img src="images/ajax-loader.gif">'); //show loading image
        $("#shopping-cart-results" ).load( "cart_process.php", {"load_cart":"1"});
      
            e.preventDefault();
        }); 


das FormularArray wird auch über ajax geladen:

PHP-Code:

if(isset($_POST["load_cart"]) && $_POST["load_cart"]==1)
{

      if(isset($_SESSION["products"]) && count($_SESSION["products"])>0){ //if we have session variable
        $cart_box = '<form class="form-to-update"><ul class="cart-products-loaded">';
        $total = 0;
        foreach($_SESSION["products"] as $product){ //loop though items and prepare html content
            
            //set variables to use them in HTML content below
            $product_name = $product["product_name"]; 
            $product_price = $product["product_price"];
            $product_code = $product["product_code"];
            $product_qty = $product["qty"];
            
            $cart_box .=  "<li><span>Ihr Produkt: $product_name </span><span>PS: $product_code <input type=\"hidden\" name=\"productCode[]\" value=\"".$product_code."\" /></span> <span>Anzahl : <input type=\"text\" name=\"quantity[]\" value=\"".$product_qty."\" style=\"width: 30px;\" /></span><span>Einzelpreis :$currency ".sprintf("%01.2f", $product_price)." </span> <span>Zwischensumme: $currency ".sprintf("%01.2f", ($product_price * $product_qty)). "</span> <span><a href=\"#\" class=\"remove-item\" data-code=\"".trim($product_code)."\"><img src=\"./themes/shop/images/trash.png\" border=\"0\" /></a></span></li>";
            $subtotal = ($product_price * $product_qty);
            $total = ($total + $subtotal);
        }
    
        $cart_box .= "</ul>";
        $cart_box .= '<div class="clearfix"></div><div class="cart-products-total">Total : '.$currency.sprintf("%01.2f",$total).' <button type="submit" class="warenkorb-aktualisieren">aktualisieren</button></form> <a href="https://www.vah.de/shop/zur-kasse" title="zur Kasse">zur Kasse</a></div>';
        die($cart_box); //exit and output content
    }else{
        die("<div class='empty'>Ihr Warenkorb ist leer</div>"); //we have empty cart
    }
} 


Nun wird leider immer nur FormularArray mit dem letzten Wert von productCode weitergegeben:

PHP-Code:

// cart_process.php

if(isset($_POST) AND is_array($_POST['productCode'])) {
                               
       foreach($_POST['productCode'] as $key => $value) {

                                          
        if(isset($_SESSION["products"])){ 
                       
                $_SESSION["products"][$value]['qty'] = $_POST['quantity'][$key]; //unset old item
                        
        }
        
   } 


Ich komme da nicht weiter. Vielleicht weiß jemand eine Lösung.

Und die productCode-Variable im ersten Abschnitt enthält was?

PHP-Code:

$("#shopping-cart-results").on('submit', '.form-to-update', function(e) {
        
    
           
 var form_data = $(this).serialize();    
                  alert(form_data); 
            $.ajax({ 
                url: "cart_process.php",
                type: "post",
        
                dataType:"json",        
 
                data: form_data
                             
                       
                        // other data
                    
            });
            
      $("#shopping-cart-results").html('<img src="images/ajax-loader.gif">'); //show loading image
        $("#shopping-cart-results" ).load( "cart_process.php", {"load_cart":"1"});
      
            e.preventDefault();
        });