paypal_payments_controller.rb

.....
 # create a transaction which records the details of the notification
    object.txns.create(:transaction_id => ipn.transaction_id,
                       :amount => ipn.gross,
                       :fee => ipn.fee,
                       :currency_type => ipn.currency,
                       :status => ipn.status,
                       :received_at => ipn.received_at)
 # if ipn.acknowledge
    ack = nil
    begin
      ack = ipn.instance_eval do
        payload =  raw

        puts "PayPal::pp_acknowledge payload = #{payload.inspect} "

        uri = URI.parse('https://www.sandbox.paypal.com/cgi-bin/webscr')
        request_path = "#{uri.path}?cmd=_notify-validate"

        puts "PayPal::pp_acknowledge before  create a new post"

        request = Net::HTTP::Post.new(request_path)
        request['Content-Length'] = "#{payload.size}"
        request['User-Agent']     = "paypal-ruby -- http://rubyforge.org/projects/paypal/"

        http = Net::HTTP.new(uri.host, uri.port)

        http.verify_mode    = OpenSSL::SSL::VERIFY_NONE unless @ssl_strict
        http.use_ssl        = true

        puts "PayPal::pp_acknowledge before  request"

        request = http.request(request, payload)

        puts "PayPal::pp_acknowledge request = #{request.inspect} "
        puts "PayPal::pp_acknowledge request body = #{request.body.inspect} "

        raise StandardError.new("Faulty paypal result: #{request.body}") unless ["VERIFIED", "INVALID"].include?(request.body)
        request.body == "VERIFIED"
      end
    rescue Exception => e
      logger.info "Exception! #{e.message}"
    end

   if ack
      case ipn.status
      when "Completed"
...