diff --git a/prijs-per-postcode.php b/prijs-per-postcode.php
index 30fbb32..b9238b8 100644
--- a/prijs-per-postcode.php
+++ b/prijs-per-postcode.php
@@ -12,12 +12,15 @@ require_once plugin_dir_path(__FILE__) . "session_dialog.php";
 require_once plugin_dir_path(__FILE__) . "admin.php";
 require_once plugin_dir_path(__FILE__) . "pppr_cookie.php";
 
+
 if (!defined("ABSPATH")) {
     echo "big bag of potatoes";
     exit();
 }
 
-
+/*
+ * Create salt 
+ */
 register_activation_hook( __FILE__, 'create_pppr_salt' );
 if ( ! defined( 'WP_PPPR_SALT' ) ) {
     $salt_file = __DIR__ . '/wp-pppr-salt.php'; 
@@ -33,6 +36,9 @@ add_filter("woocommerce_sale_flash", "__return_null");
 add_filter('woocommerce_show_variation_price', '__return_true');   
 
 
+/*
+ * Init the plugin
+ */
 add_action("init", function() {
     $uri = $_SERVER["REQUEST_URI"];
     init_postcode_handlers($uri);
@@ -42,10 +48,21 @@ add_action("init", function() {
 );
 
 
-// Set endpoint (postcode-modal/v1/submit) for the modal form.
-add_action("rest_api_ini", "register_modal_api");
+/*
+ *  Set endpoint (postcode-modal/v1/submit) for the modal form.
+ */
+add_action("rest_api_init", function () {
+    register_rest_route( 'postcode-modal/v1', '/submit', array(
+        'methods'             => 'POST',
+        'callback'            => 'handle_postcode_modal',
+        'permission_callback' => '__return_true',
+    ) );
+});
 
-/*Add local orice field to variation product.*/
+
+/* 
+ * Add local orice field to variation product.
+ */
 add_action("woocommerce_variation_options_pricing", 
     function($loop, $variation_data, $variation)
     {
@@ -64,7 +81,9 @@ add_action("woocommerce_variation_options_pricing",
 );
 
 
-/*Save the local price on product save */
+/*
+ * Save the local price on product save in the admin
+ */
 add_action("woocommerce_save_product_variation",
     function ($variation_id, $i)
     {
@@ -79,7 +98,11 @@ add_action("woocommerce_save_product_variation",
     }, 10, 2,
 );
 
-// Replace "Reguliere prijs" with "Prijs overige regios" in variation prodict admin
+
+/* 
+ * Replace "Reguliere prijs" with "Prijs overige regios" 
+ * in variation prodict admin
+ */
 add_filter( "gettext", function( $translated_text, $text, $domain,) {
         if (
             "woocommerce" === $domain &&
@@ -96,7 +119,9 @@ add_filter( "gettext", function( $translated_text, $text, $domain,) {
 );
 
 
-/* Filter out variations whwre the price is either 0 or ''
+/* 
+ * Filter out variations whwre the price is 
+ * either 0 or '' in the dropdown menu product page
  */
 add_filter("woocommerce_variation_is_visible",
     function (
@@ -127,31 +152,34 @@ add_filter("woocommerce_variation_is_visible",
 );
 
 
-/* Dynamically recalculates the cart total by overriding the standard price 
+/* 
+ * Dynamically recalculates the cart total by overriding the standard price 
  * with a region-specific _local_price for variations when 
  * the user's location matches the PPPR cookie criteria 
  */
-add_action("woocommerce_before_calculate_totals", 
-    function($cart)
+add_action("woocommerce_before_calculate_totals", function($cart)
     {
         if (is_admin() && !defined("DOING_AJAX")) {
             return;
         }
 
-        foreach ($cart->get_cart() as $cart_item) {
+        foreach ($cart->get_cart() as $cart_item) 
+        {
             $product = $cart_item["data"];
             $variation_id = $product->is_type("variation")
                 ? $product->get_id()
                 : 0;
 
-            if ( $variation_id && isset($_COOKIE["PPPR"]) && pppr_is_local() ) {
+            if ( $variation_id && isset($_COOKIE["PPPR"]) && pppr_is_local() ) 
+            {
                 $local_price = get_post_meta(
                     $variation_id,
                     "_local_price",
                     true,
-            );
+                );
 
-                if ($local_price) {
+                if ($local_price) 
+                {
                     $product->set_price($local_price);
                 }
             }
@@ -160,6 +188,9 @@ add_action("woocommerce_before_calculate_totals",
 );
 
 
+/* 
+ * Filter to display the regular or local price on teh product page. 
+ */
 add_filter( "woocommerce_get_price_html",
     function($price_html, $product)
     {
@@ -181,7 +212,9 @@ add_filter( "woocommerce_get_price_html",
     }, 10, 2,
 );
 
-/* Enforces region-locking by clearing the cart and redirecting users to 
+
+/* 
+ * Enforces region-locking by clearing the cart and redirecting users to 
  * the shop page if their location cookie is invalid or expired when 
  * accessing key WooCommerce pages. 
  */
@@ -215,6 +248,43 @@ add_action("template_redirect",
 );
 
 
+/* 
+ * Chack or postcode is still valid when pressing the buy button 
+ */
+add_action( 'woocommerce_after_checkout_validation', function( $data, $errors ) {
+    // 1. Controleer of de cookie bestaat en geldig is
+    if ( ! isset( $_COOKIE['PPPR'] ) || ! verify_pppr_cookie_string() ) {
+        $errors->add( 
+            'pppr_cookie_invalid', 
+            __( '<strong>Fout:</strong> Sessie verlopen. Vernieuw de pagina en vul je postcode opnieuw in.', 'woocommerce' ) 
+        );
+        return; // Stop hier, geen zin om verder te checken
+    }
+
+    $pppr_data = get_PPPR_data();
+
+    if ( ! $pppr_data || empty( $pppr_data['postcode'] ) ) {
+        $errors->add( 
+            'pppr_data_missing', 
+            __( '<strong>Fout:</strong> Kon postcode niet laden.', 'woocommerce' ) 
+        );
+        return;
+    }
+
+    // 3. Normalizeer postcodes (gebruik de juiste variabelen!)
+    $cookie_pc   = strtoupper( str_replace( ' ', '', $pppr_data['postcode'] ) );
+    $shipping_pc = strtoupper( str_replace( ' ', '', $data['shipping_postcode'] ) );
+
+    // 4. Vergelijk
+    if ( $cookie_pc !== $shipping_pc ) {
+        wc_add_notice( 
+            __( '<strong>Fout:</strong> Afleverpostcode komt niet overeen met de eerder ingevulde postcode.', 'woocommerce' ), 
+            'error' 
+        );
+    }
+}, 10, 2 );
+
+
 function get_shop_url () {
   return  (function_exists('wcml_get_store_url')) 
     ? wcml_get_store_url() // WPML WooCommerce Multilingual