Why my controller cannot get request from view?

I want to insert some data to database, I need id that I can get from my route and quantity. But my quantity keep define as null. This is my view

<form  method="POST" action="" enctype="multipart/form-data" >
              <input type="hidden" name="_token" value="">
              <div class="form-group">
                    <label for="exampleInputEmail1">Jumlah Beli :</label>
                    <input type="name" class="form-control" name ="quantity" id="quantity" placeholder="Jumlah">
                  </div>
              
              <div class="mt-4">
                <div class="btn btn-default btn-lg btn-flat">
                  <i class=" fa-lg mr-2"></i> <a href="">
                  Beli Produk </a>
                </div>
                </form>

and this is my Controller

public function tambah(Request $request, $id)
    {
        $idtoko = Store::select('id')->where('users_id',Auth::user()->id)->first();
        $transaksi = new Transaction();
        $transaksi->quantity = $request->get('quantity');
        $transaksi->stores_id = $idtoko->id;
        $transaksi->save();
    }

And this is my route Route::get('/beli/{id}','KeranjangController@tambah');

via Chebli Mohamed