laravel session route redirection error on multiple input fields

I have the following controller whenever i hit submit it redirects me to sales. Where as it should return admin.invoice.index page rather than sale.index. can any one please help?

  $data = array();
    for ($i=0; $i < count($request['product_id']); ++$i) 
    {
     $sales= new Sale;        
     $sales->product_id = $request['product_id'][$i];
     $sales->qty= $request['qty'][$i];
     $sales->user_id = Auth::user()->id;
     $sales->save(); 
     $product = new Product;
     $product->where('id', '=', $request['product_id'][$i])->decrement('stock', $request['qty'][$i]);
     $data[]['sales'] = $sales;
     $data[]['product'] = $product;

 }

 $data = [];
 if ($request->session()->has('data')) {
    $data = $request->session()->get('data');


}
Session::flash('success', 'Sale is successfully');
return view('admin.invoice.index')->with('data', $data);

}

via Chebli Mohamed