def subscription_pricing_tiers(app_id)
      @subscription_pricing_tiers ||= begin
        r = request(:get, "ra/apps/#{app_id}/iaps/pricing/matrix/recurring")
        data = parse_response(r, "data")["pricingTiers"]
        data.map { |tier| Spaceship::Tunes::IAPSubscriptionPricingTier.factory(tier) }
      end
    end
def subscription_pricing_tiers(app_id)
      @subscription_pricing_tiers ||= begin
        r = request(:get, "ra/apps/#{app_id}/iaps/pricing/matrix/recurring")
        data = parse_response(r, "data")["pricingTiers"]
        data.map { |tier| Spaceship::Tunes::IAPSubscriptionPricingTier.factory(tier) }
      end
    end
Loads the full In-App-Purchases-Pricing-Matrix
   note: the matrix is the same for any app_id

 @param app_id (String) The Apple ID of any app
 @return ([Spaceship::Tunes::IAPSubscriptionPricingTier]) An array of pricing tiers