    # File lib/active_merchant/billing/integrations/paypal/notification.rb, line 138
              def acknowledge
                payload =  raw

                response = ssl_post(Paypal.service_url + '?cmd=_notify-validate', payload,
                  'Content-Length' => "#{payload.size}",
                  'User-Agent'     => "Active Merchant -- http://activemerchant.org"
                )

                raise StandardError.new("Faulty paypal result: #{response}") unless ["VERIFIED", "INVALID"].include?(response)

                response == "VERIFIED"
              end