diff --git a/openapi.yaml b/openapi.yaml
index 84c1844a..d0b519ac 100644
--- a/openapi.yaml
+++ b/openapi.yaml
@@ -6442,6 +6442,14 @@ paths:
           responses:
             '200':
               description: Success
+            '400':
+              description: Invalid booking input or a product blocked by active customer rules
+              content:
+                application/json:
+                  schema:
+                    oneOf:
+                      - $ref: '#/components/schemas/CustomerRuleProductRestrictedResponse'
+                      - type: object
         put:
           tags:
             - Bookings
diff --git a/services/nginx/app/openapi.yaml b/services/nginx/app/openapi.yaml
index e6042201..2b3c0d70 100644
--- a/services/nginx/app/openapi.yaml
+++ b/services/nginx/app/openapi.yaml
@@ -6771,6 +6771,14 @@ paths:
           responses:
             '200':
               description: Success
+            '400':
+              description: Invalid booking input or a product blocked by active customer rules
+              content:
+                application/json:
+                  schema:
+                    oneOf:
+                      - $ref: '#/components/schemas/CustomerRuleProductRestrictedResponse'
+                      - type: object
         put:
           tags:
             - Bookings
diff --git a/services/nginx/app/routes/orderBookingRoute.php b/services/nginx/app/routes/orderBookingRoute.php
index 8dff903a..b3c54a96 100644
--- a/services/nginx/app/routes/orderBookingRoute.php
+++ b/services/nginx/app/routes/orderBookingRoute.php
@@ -3,6 +3,7 @@
 namespace routes;
 
 use classes\authentication;
+use classes\customer_rule_product_restriction_service;
 use classes\email;
 use classes\order_bookings_counts_cache;
 use classes\order_bookings_list_cache;
@@ -52,6 +53,7 @@ class orderBookingRoute
                 $customer_number,
                 (int)$department->id
             ); // Array of order_items_o objects
+            $this->requireBookingItemsAllowedForCustomer($customer_number, $items);
             /**
              * Input data
              */
@@ -835,6 +837,39 @@ class orderBookingRoute
         return $items;
     }
 
+    /**
+     * Enforce customer product rules again at the booking write boundary.
+     *
+     * The browser uses the same rules for guidance, but a stale or crafted
+     * request must not be able to persist a restricted base product or add-on.
+     *
+     * @param list<array<string, mixed>> $items
+     */
+    private function requireBookingItemsAllowedForCustomer(users_o $customer, array $items): void
+    {
+        global $response;
+
+        $customerNumber = (int)$customer->customer_number->value();
+        $restrictionService = new customer_rule_product_restriction_service();
+        foreach ($items as $item) {
+            $violation = $restrictionService->violationForCustomerProduct(
+                $customerNumber,
+                (int)($item['id'] ?? 0)
+            );
+            if ($violation === null) {
+                continue;
+            }
+
+            $response->error([
+                'code' => $violation['code'],
+                'message' => $violation['message'],
+                'product_id' => $violation['product_id'],
+                'rules' => $violation['rules'],
+                'collections' => $violation['collections'],
+            ], 400);
+        }
+    }
+
     /**
      * @throws Exception
      */
diff --git a/services/nginx/app/tests/Api/OrderBookingsCreateApiTest.php b/services/nginx/app/tests/Api/OrderBookingsCreateApiTest.php
index 3adaefcb..c9d959da 100644
--- a/services/nginx/app/tests/Api/OrderBookingsCreateApiTest.php
+++ b/services/nginx/app/tests/Api/OrderBookingsCreateApiTest.php
@@ -49,6 +49,33 @@ function order_booking_create_department_price(int $departmentId, int $productId
     $statement->close();
 }
 
+function order_booking_configure_customer_rule_product(string $attribute, int $productId): void
+{
+    new \classes\customer_rule_product_restriction_service();
+    $db = api_test_runtime()->db();
+    $safeAttribute = $db->real_escape_string($attribute);
+    $result = $db->query(
+        "SELECT id FROM customer_rule_product_collections
+         WHERE attribute = '{$safeAttribute}' ORDER BY sort_order, id LIMIT 1"
+    );
+    $collectionId = $result && $result->num_rows > 0 ? (int)$result->fetch_assoc()['id'] : 0;
+    if ($collectionId < 1) {
+        $db->query(
+            "INSERT INTO customer_rule_product_collections (attribute, name, sort_order)
+             VALUES ('{$safeAttribute}', 'Booking API exact restriction', 0)"
+        );
+        $collectionId = (int)$db->insert_id;
+    }
+    $db->query(
+        "INSERT IGNORE INTO customer_rule_product_collection_products (collection_id, product_id)
+         VALUES ({$collectionId}, {$productId})"
+    );
+    api_fixtures()->cleanupDeleteWhere('customer_rule_product_collection_products', [
+        'collection_id' => $collectionId,
+        'product_id' => $productId,
+    ]);
+}
+
 it('lets customers create their own order bookings without booking permissions', function (): void {
     api_test_covers('POST /order-bookings', 'auth');
 
@@ -219,3 +246,80 @@ it('lets department-scoped users create order bookings for another customer', fu
 
     api_fixtures()->cleanupDeleteById('order_bookings', $bookingId);
 });
+
+it('rejects a restricted base product when creating an order booking', function (): void {
+    api_test_covers('POST /order-bookings', 'customer-rule-validation');
+
+    $session = api_fixtures()->createUserSession(['user']);
+    $department = order_booking_create_department('Restricted Booking Product Department');
+    $product = api_fixtures()->createProduct(['name' => 'Restricted Booking Base Product']);
+    api_fixtures()->addCustomerAttribute((int)$session['user']['id'], 'restrictSpotFree');
+    order_booking_configure_customer_rule_product('restrictSpotFree', (int)$product['id']);
+
+    $response = api_client()->post(
+        '/order-bookings',
+        order_booking_create_payload($session['user'], $department, $product, 'RULEBASE1'),
+        $session['headers']
+    );
+
+    $response
+        ->assertStatus(400)
+        ->assertEnvelope()
+        ->assertSuccess(false)
+        ->assertMessage(\classes\customer_product_rule_service::BLOCK_MESSAGE);
+    expect($response->data())
+        ->toMatchArray([
+            'code' => 'CUSTOMER_RULE_PRODUCT_RESTRICTED',
+            'product_id' => (int)$product['id'],
+        ]);
+});
+
+it('rejects a booking when an add-on item is restricted', function (): void {
+    api_test_covers('POST /order-bookings', 'customer-rule-validation');
+
+    $session = api_fixtures()->createUserSession(['user']);
+    $department = order_booking_create_department('Restricted Booking Addon Department');
+    $baseProduct = api_fixtures()->createProduct(['name' => 'Allowed Booking Base Product']);
+    $addonProduct = api_fixtures()->createProduct(['name' => 'Restricted Booking Add-on']);
+    api_fixtures()->addCustomerAttribute((int)$session['user']['id'], 'restrictAdditionalServices');
+    order_booking_configure_customer_rule_product('restrictAdditionalServices', (int)$addonProduct['id']);
+    $payload = order_booking_create_payload($session['user'], $department, $baseProduct, 'RULEADD1');
+    $payload['items'][] = ['id' => (int)$addonProduct['id'], 'quantity' => 1];
+
+    $response = api_client()->post('/order-bookings', $payload, $session['headers']);
+
+    $response
+        ->assertStatus(400)
+        ->assertEnvelope()
+        ->assertSuccess(false);
+    expect($response->data())
+        ->toMatchArray([
+            'code' => 'CUSTOMER_RULE_PRODUCT_RESTRICTED',
+            'product_id' => (int)$addonProduct['id'],
+        ]);
+});
+
+it('allows an exact product that is not included in the active customer restriction', function (): void {
+    api_test_covers('POST /order-bookings', 'customer-rule-validation');
+
+    $session = api_fixtures()->createUserSession(['user']);
+    $department = order_booking_create_department('Allowed Booking Rule Department');
+    $allowedProduct = api_fixtures()->createProduct(['name' => 'Allowed Booking Exact Product']);
+    $restrictedProduct = api_fixtures()->createProduct(['name' => 'Other Restricted Booking Product']);
+    api_fixtures()->addCustomerAttribute((int)$session['user']['id'], 'restrictSpotFree');
+    order_booking_configure_customer_rule_product('restrictSpotFree', (int)$restrictedProduct['id']);
+
+    $response = api_client()->post(
+        '/order-bookings',
+        order_booking_create_payload($session['user'], $department, $allowedProduct, 'RULEOK1'),
+        $session['headers']
+    );
+
+    $response
+        ->assertStatus(200)
+        ->assertEnvelope()
+        ->assertSuccess();
+    $bookingId = (int)($response->data()['id'] ?? 0);
+    expect($bookingId)->toBeGreaterThan(0);
+    api_fixtures()->cleanupDeleteById('order_bookings', $bookingId);
+});