You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: pro_subscription_controller.rb
    path of file: ./repos/kitsu-server/app/controllers
    
    the code of the file until where you have to start completion: class ProSubscriptionController < ApplicationController
  include CustomControllerHelpers

  before_action :check_feature_flag!
  before_action :authenticate_user!

  def ios
    receipt = AppleReceiptService.new(params[:receipt])
    render json: ProSubscription::AppleSub
    
  def destroy
    case user.pro_subscription.billing_service
    when :apple_ios
      # We cannot cancel an iOS subscription â€” cancellation must be done through Apple or in-app
      render_jsonapi_error 400, 'Cannot cancel an iOS subscription outside of the App Store'
    when :stripe, :google_play
      user.pro_subscription.destroy!
      render json: {}
    end
  end