def self.billing(subclass = nil, credentials: nil)
        require 'google/apis/cloudbilling_v1'

        if subclass.nil?
          @@billing_api[credentials] ||= MU::Cloud::Google::GoogleEndpoint.new(api: "CloudbillingV1::CloudbillingService", scopes: ['cloud-platform', 'cloud-billing'], credentials: credentials, masquerade: MU::Cloud::Google.credConfig(credentials)['masquerade_as'])