In Google Cloud Platform I can`t set metadata and get windows VM password using .net SDK

Question

I`m using .NET SDK and want to get the windows password.

I have read this document and wrote code based on the Java example.

But, I have got this error on serial port 1 when executing SetMetadataRequest and I can`t get encrypted password on serial port 4.

-------------------error message when setting metadata--------------------------------

" 2019/09/16 12:28:36 GCEWindowsAgent: ERROR accounts.go:275: invalid character ':' after top-level value"

My code is:

using Google.Apis.Auth.OAuth2;
using Google.Apis.Compute.v1;
using Google.Apis.Compute.v1.Data;
using Google.Apis.Services;
using java.math;
using java.security;
using java.security.spec;
using java.util;
using Newtonsoft.Json.Linq;
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;

namespace GoogleHelper
{
    internal class GoogleVmHelper : VmTaskInterface
    {

        private ComputeService _Client;

        public async Task<bool> SetMetadata()
        {

// //---after instantiate of ComputeService _Client////

            InstancesResource.GetRequest describeServerReq = _Client.Instances.Get("projectid", "region", "serverid");
            Data.Instance describeServerRes = await describeServerReq.ExecuteAsync();
            Metadata oldMetaData = describeServerRes.Metadata;

            // Generate the public/private key pair for encryption and decryption.
            KeyPair keys = generateKeys();
            var buildedKeys = buildKeyMetadata(keys);

            //Replace Metadata
            string newItemString = buildedKeys.ToString();

            // Get the list containing all of the Metadata entries for this instance.
            var items = oldMetaData.Items;

            // If the instance has no metadata, items can be returned as null.
            if (items == null)
            {
                items = new List<Metadata.ItemsData>();
                oldMetaData.Items = items;
            }

            // Find the "windows-keys" entry and update it.
            bool isFound = false;
            foreach (var item in items)
            {
                if (item.Key == "windows-keys")
                {
                    // Replace item's value with the new entry.
                    // To prevent race conditions, production code may want to maintain a
                    // list where the oldest entries are removed once the 32KB limit is
                    // reached for the metadata entry.
                    item.Value = newItemString;
                    isFound = true;
                    break;
                }
            }

            if (!isFound)
            {
                // "windows.keys" entry doesn't exist in the metadata - append it.
                // This occurs when running password-reset for the first time on an instance.
                var addItem = new Metadata.ItemsData();
                addItem.Key = "windows-keys";
                addItem.Value = newItemString;
                items.Add(addItem);
            }

            oldMetaData.Items = items;

            //Set Metadata
            var setMetadataReq = new InstancesResource.SetMetadataRequest(_Client, oldMetaData, _Profile.ProjectID, _Task.Region, _Task.ServerID);
            var serMEtaDataRes = await setMetadataReq.ExecuteAsync();

            await System.Threading.Tasks.Task.Delay(30000);

            //GetPassword
            var getSerialPortOutputReq = new InstancesResource.GetSerialPortOutputRequest(_Client, _Profile.ProjectID, _Task.Region, _Task.ServerID);
            getSerialPortOutputReq.Port = 4;
            var getSerialPortOutputRes = await getSerialPortOutputReq.ExecuteAsync();

            //EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY
            var entries = getSerialPortOutputRes.Contents;
            //EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY EMPTY

            return true;
        }


        private KeyPair generateKeys()
        {
            KeyPairGenerator keyGen = KeyPairGenerator.getInstance("RSA");

            // Key moduli for encryption/decryption are 2048 bits long.
            keyGen.initialize(2048);

            return keyGen.genKeyPair();
        }

        private JObject jsonEncode(KeyPair keys)
        {
            KeyFactory factory = KeyFactory.getInstance("RSA");

            // Get the RSA spec for key manipulation.
            RSAPublicKeySpec pubSpec = factory.getKeySpec(keys.getPublic(), typeof(RSAPublicKeySpec)) as RSAPublicKeySpec;

            // Extract required parts of the key.
            BigInteger modulus = pubSpec.getModulus();
            BigInteger exponent = pubSpec.getPublicExponent();

            // Strip out the leading 0 byte in the modulus.
            byte[] arr = Arrays.copyOfRange(modulus.toByteArray(), 1, modulus.toByteArray().Length);

            JObject returnJson = new JObject();

            // Encode the modulus, add to returned JSON object.
            String modulusString = Convert.ToBase64String(arr).Replace("\n", "");
            returnJson.Add("modulus", modulusString);

            // Encode exponent, add to returned JSON object.
            String exponentString = Convert.ToBase64String(exponent.toByteArray()).Replace("\n", "");

            returnJson.Add("exponent", exponentString);

            return returnJson;
        }


        private JObject buildKeyMetadata(KeyPair pair)
        {
            // Encode the public key into the required JSON format.
           var metadataValues =  jsonEncode(pair);

            // Add username and email.
            metadataValues.Add("userName", "myusername");
            metadataValues.Add("email", "myemal");

            //Create the date on which the new keys expire.
            //DateTime now = new DateTime();
            var expiredDate = DateTime.Now + TimeSpan.FromMinutes(5);

            //Format the date to match rfc3339.
            DateTime utcTime = System.TimeZoneInfo.ConvertTimeToUtc(expiredDate);
            String dateString = utcTime.ToString("yyyy-MM-dd'T'HH:mm:ss'Z'");
            //Encode the expiration date for the returned JSON dictionary.
            metadataValues.Add("expireOn", dateString);

            return metadataValues;
        }

    }    
}