diff --git a/shop/app/actions/checkout.ts b/shop/app/actions/checkout.ts
new file mode 100644
index 0000000..6ea1540
--- /dev/null
+++ b/shop/app/actions/checkout.ts
@@ -0,0 +1,141 @@
+'use server'
+
+import { createClient } from '@/lib/supabase/server';
+import { createHash } from 'crypto';
+import { buildCustomerSnapshot, buildOrderSnapshot } from '@/lib/license-transform';
+import { getProducts, getCategories } from '@/lib/actions/products';
+
+function generateOrderNumber(prefix: 'BE' | 'AE' = 'AE'): string {
+  const year = new Date().getFullYear();
+  const rand = Math.floor(10000 + Math.random() * 90000);
+  return `${prefix}-${year}-${rand}`;
+}
+
+function hashOrderPayload(endCustomerId: string, items: any[]): string {
+  const str = endCustomerId + JSON.stringify(items);
+  return createHash('sha256').update(str).digest('hex');
+}
+
+export async function checkoutAction(params: {
+  items: any[];
+  endCustomerId: string;
+  customerProfile?: any;
+}) {
+  const { items, endCustomerId, customerProfile } = params;
+  const supabase = await createClient();
+
+  // 1. Session & Auth Check
+  const { data: { user } } = await supabase.auth.getUser();
+  if (!user) {
+    throw new Error('Not authenticated');
+  }
+
+  const { data: dbUser } = await supabase
+    .from('users')
+    .select('role, company_id')
+    .eq('id', user.id)
+    .single();
+
+  const isAdminUser = dbUser?.role === 'admin';
+  if (!isAdminUser && !dbUser?.company_id) {
+    throw new Error('Kein Unternehmen zugewiesen. Zugriff verweigert.');
+  }
+
+  // 2. Idempotency Guard
+  const orderHash = hashOrderPayload(endCustomerId, items);
+  const fiveMinutesAgo = new Date(Date.now() - 5 * 60_000).toISOString();
+
+  const { data: existingOrders } = await supabase
+    .from('orders')
+    .select('id')
+    .eq('user_id', user.id)
+    .eq('order_hash', orderHash)
+    .gte('created_at', fiveMinutesAgo);
+
+  if (existingOrders && existingOrders.length > 0) {
+    return { success: true, orderIds: existingOrders.map(o => o.id), duplicated: true };
+  }
+
+  // Fetch End Customer Stammdaten
+  const { data: endCustomer, error: customerErr } = await supabase
+    .from('end_customers')
+    .select('*')
+    .eq('id', endCustomerId)
+    .single();
+
+  if (customerErr || !endCustomer) {
+    throw new Error('Endkunde nicht gefunden.');
+  }
+
+  const customerSnapshot = buildCustomerSnapshot(customerProfile || {}, endCustomer);
+
+  const products = await getProducts();
+  const categories = await getCategories();
+
+  // 3. Checkout Split
+  const purchaseItems = items.filter(
+    (item: any) => item.billingInterval === 'one_time' || item.billingType === 'purchase'
+  );
+  const subscriptionItems = items.filter(
+    (item: any) => item.billingInterval === 'monthly' || item.billingType === 'subscription'
+  );
+
+  const orderIds: string[] = [];
+
+  const createOrderGroup = async (groupItems: any[], type: 'purchase' | 'subscription', paymentMethod: string) => {
+    if (groupItems.length === 0) return;
+
+    const orderItemsList: any[] = [];
+    let total = 0;
+
+    for (const item of groupItems) {
+      const itemSnapshot = buildOrderSnapshot(
+        item.selections,
+        products,
+        categories,
+        type === 'purchase' ? 'one_time' : 'monthly',
+        item.moduleQuantities
+      );
+      orderItemsList.push(...itemSnapshot.items);
+      total += itemSnapshot.total;
+    }
+
+    const orderSnapshot = {
+      schema_version: 1,
+      billing_cycle: type === 'purchase' ? 'one_time' : 'monthly',
+      items: orderItemsList,
+      total: total,
+      tax_rate: 19,
+      tax_amount: Math.round(total * 0.19 * 100) / 100,
+      subtotal: Math.round((total / 1.19) * 100) / 100
+    };
+
+    const orderNumber = generateOrderNumber(type === 'purchase' ? 'AE' : 'BE');
+
+    const { data: order, error: orderError } = await supabase
+      .from('orders')
+      .insert([{
+        user_id: user.id,
+        company_id: dbUser?.company_id || null,
+        order_number: orderNumber,
+        order_hash: orderHash,
+        end_customer_id: endCustomerId,
+        total_price: total,
+        customer_data: customerSnapshot,
+        order_data: orderSnapshot,
+        type: type,
+        payment_method: paymentMethod,
+        status: 'pending'
+      }])
+      .select()
+      .single();
+
+    if (orderError) throw orderError;
+    orderIds.push(order.id);
+  };
+
+  await createOrderGroup(purchaseItems, 'purchase', 'invoice');
+  await createOrderGroup(subscriptionItems, 'subscription', 'sepa');
+
+  return { success: true, orderIds, duplicated: false };
+}