ActiveAdmin Routing Error when adding member_action

Having come across the following: Routing “member_action” with activeadmin. I have followed active admin documentation for adding a customised action: Custom Action. My setup is as followed:

ActiveAdmin.register Charity do

  index do
    selectable_column
    id_column
    column :name
    column :website
    column :location
    column :user_id
    column :aasm_state
    actions
  end


  filter :name
  filter :location
  filter :assm_state

  member_action :approve, :method => :put do
    Charity.find(params[:id])
    redirect_to :back
  end

  action_item :approve, method: :put, only: :show do
    link_to 'Approve', approve_admin_charity_path(params[:id])
  end


  controller do
    def approve
      puts "foo"
    end
  end

end

Routes.rb

approve_admin_charity PUT   /admin/charities/:id/approve(.:format)               
admin/charities#approve

error when i click the link below

Started GET "/admin/charities/33/approve" for 127.0.0.1 at 2015-06-21 03:29:09 -0400

ActionController::RoutingError (No route matches [GET] "/admin/charities/33/approve"):

Can anyone suggest what I maybe doing wrong here thanks