need some help with routes maybe

Im making a Cart for my site, so I make Orders Controller to manage Orders

so inside I do

  def add_product     @product = Product.find(params[:id])     @order = Order.find_by_client_id(current_user.id)     @order.products << @product   end

on Product view/show I place <%= link_to t(:add_to_cart), order_add_product_path(@product) %>

config/routes   resources :orders do     get :add_product   end

But i kept getting

http://localhost:3000/orders/3/add_product ActiveRecord::RecordNotFound in OrdersController#add_product Couldn't find Product without an ID

model: orders has_and_belongs_to_many :products products has_and_belongs_to_many :orders