gistfile1.rb

ActiveAdmin.register AdvocacyPage do
  menu label: 'Advocacy Page', url: "/admin/advocacy_pages/edit"
  breadcrumb { [] }

  permit_params :heading, :description

  actions :update
  
  controller do
    def resource
      AdvocacyPage.instance
    end

    def update
      update! { edit_admin_advocacy_pages_url }
    end
  end

  collection_action :edit, :method => :get do
  end

  form do |f|
    f.inputs "Details" do
      f.input :heading
      f.input :description
    end
    f.actions do
      f.action :submit
    end
  end
end