# 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