'shop_code' => 'required|exists:shops,code',
            'product_id' => 'nullable|exists:products,id',
            'units_sold' => 'required|integer|min:1',
            'cash_collected' => 'required|numeric|min:0',
            'refill_quantity' => 'required|integer|min:0',
            'payment_method' => 'required|in:cash,credit',
            'add_bonus_product' => 'nullable|boolean',
        ]);
        
        // Find shop by code and verify it belongs to this agent
        $shop = Shop::where('code', $validated['shop_code'])
            ->where('agent_id', $agentId)
            ->firstOrFail();
        
        // Use provided product or get first active product
        $productId = $validated['product_id'] ?? null;
        if ($productId) {
            $product = Product::findOrFail($productId);
        } else {
            $product = Product::active()->first();
            if (!$product) {
                return redirect()->back()->with('error', 'No active products found in the system.');
            }
        }