I got error but laraval.log is empty

I got this error

Whoops, looks like something went wrong.

but laravel.log file is empty. the problem is not with writing in this file because I get other errors.

Is there any other files laravel save logs in it?

what I want to do :

backend/agent/products/index.blade.php

<form action="" method="post" class="horizontal-form">
    
    
    <div class="row">
        <div class="col-md-3">
            <label for="quantity">تعداد</label>
            <input id="quantity" name="quantity" class="form-control text-center" type="text" value="1">
        </div>

        <div class="col-md-9">
            <label class="control-label" for="seller">فروشنده</label>
            <select name="seller" id="seller" class="form-control">
                <option value="">انتخاب کنید</option>
                @foreach ($product->users as $price_index => $price)
                <option value=""> به قیمت  تومان</option>
                @endforeach
                </select>
         </div>
     </div>

     @foreach ($errors->all() as $error)
     <li></li>
     @endforeach

     <div class="row">
         <div class="col-md-12">
         <br>
         <button type="submit" class="btn btn-success">افزودن به سبد خرید</button>
      </div>
    </div>
</form>

backend/agent/ProductController.php

public function addToCart(Request $request, $id, $name)
  {
      $this->validate($request, [
        'quantity' => 'required',
        'seller' => 'required'
      ]);

      $quantity = $request->input('quantity');
      Cart::add($id, $name, $quantity, 9.99);
      return redirect()->action('Backend\Agent\ProductController@index');
  }

web.php

Route::get('products/addtocart/{id}/{name}', 'ProductController@addToCart');

via Chebli Mohamed