【rails】Active_adminの多対多の関係での投稿が出来ない

現在railsのプロジェクトで管理画面をactive_adminというgemを使って実装しておりますが、
productテーブルとcategoryテーブルの多対多の関係（category_productsという中間テーブルをはさむ）でproduct上からcategoryを投稿しようとするとemptyになってしまう。

現在以下のように実装しています。

Product model

class Product < ActiveRecord::Base
  has_many :category_products
  has_many :categories, through: :category_products
  accepts_nested_attributes_for :category_products, :allow_destroy => true
end

Category model

class Category < ActiveRecord::Base
  has_many :category_products
  has_many :products, through: :category_products
end

Product admin

ActiveAdmin.register Product do

permit_params :name, :price, :product_id, :category_id

form do |f|
    # f.semantic_errors *f.object.errors.keys
     f.inputs "Admin Details" do
      f.input :name
      f.input :price
    end
    f.inputs "products" do
      f.has_many :category_products do |t|
        t.input :category
      end
    end
    f.actions
  end 


end

category admin

ActiveAdmin.register Category do

permit_params :name

end

](e6a3ada052691e3ca1d5d5a185790983.png)

操作時のログは以下です。

Started POST "/admin/products" for ::1 at 2017-02-28 15:06:43 +0900
Processing by Admin::ProductsController#create as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"qGGzmXU9qmlh/beJywM2iXsKBS1p1bMFQocEg4X3peuNiE1Xvmm/ZMWt53CKy2uJZjtRpmAaKu/62CEnPB39zQ==", "product"=>{"name"=>"test", "price"=>"100", "category_products_attributes"=>{"0"=>{"category_id"=>"2"}}}, "commit"=>"Create Product"}
  AdminUser Load (0.4ms)  SELECT  `admin_users`.* FROM `admin_users` WHERE `admin_users`.`id` = 1  ORDER BY `admin_users`.`id` ASC LIMIT 1
Unpermitted parameter: category_products_attributes
   (0.2ms)  BEGIN
  SQL (5.1ms)  INSERT INTO `products` (`name`, `price`, `created_at`, `updated_at`) VALUES ('test', 100, '2017-02-28 06:06:43', '2017-02-28 06:06:43')
   (0.7ms)  COMMIT
Redirected to http://localhost:3000/admin/products/2
Completed 302 Found in 36ms (ActiveRecord: 6.3ms)


Started GET "/admin/products/2" for ::1 at 2017-02-28 15:06:43 +0900
Processing by Admin::ProductsController#show as HTML
  Parameters: {"id"=>"2"}
  AdminUser Load (0.3ms)  SELECT  `admin_users`.* FROM `admin_users` WHERE `admin_users`.`id` = 1  ORDER BY `admin_users`.`id` ASC LIMIT 1
  Product Load (0.4ms)  SELECT  `products`.* FROM `products` WHERE `products`.`id` = 2 LIMIT 1
   (0.5ms)  SELECT COUNT(*) FROM `active_admin_comments` WHERE `active_admin_comments`.`resource_type` = 'Product' AND `active_admin_comments`.`resource_id` = '2' AND `active_admin_comments`.`namespace` = 'admin'
  CACHE (0.0ms)  SELECT COUNT(*) FROM `active_admin_comments` WHERE `active_admin_comments`.`resource_type` = 'Product' AND `active_admin_comments`.`resource_id` = '2' AND `active_admin_comments`.`namespace` = 'admin'  [["resource_type", "Product"], ["resource_id", "2"], ["namespace", "admin"]]
  Rendered /Users/Kohei/.rbenv/versions/2.1.3/lib/ruby/gems/2.1.0/bundler/gems/activeadmin-6966a84c950b/app/views/active_admin/resource/show.html.arb (264.0ms)
Completed 200 OK in 271ms (Views: 266.8ms | ActiveRecord: 1.3ms)

現在デザインは上記のようになっておりますが、createした後にカテゴリーがDBに反映されません。
もし、解決方法などがわかる方がおりましたらご教示いただければと存じます。よろしくお願いします。