Simple code snippet showing use of Google Service Account JSON key file within ServiceAccountCredential

service_account_with_json_key.cs

// Simple code snippet showing use of Google Service Account JSON key file within ServiceAccountCredential.

using System.IO;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Calendar.v3;
using Google.Apis.Calendar.v3.Data;
using Google.Apis.Services;
using Newtonsoft.Json.Linq;

var serviceAccountJson = File.ReadAllText("<JSON-FILE-HERE>");

var o = JObject.Parse(serviceAccountJson);

var email = o["client_email"].ToString();
var privateKey = o["private_key"].ToString();

ServiceAccountCredential credential = new ServiceAccountCredential(
    new ServiceAccountCredential.Initializer(email)
    {
        Scopes = new[] { CalendarService.Scope.CalendarReadonly }
    }.FromPrivateKey(privateKey);
    
// Just an example initialising Calendar API
var service = new CalendarService(new BaseClientService.Initializer
{
    HttpClientInitializer = credential,
    ApplicationName = "APP-NAME-HERE"
});

// Then do what you like with the 'service' instance.

my code as the following very similar to above and I am getting the System.Exception - Inner Exception/Format Exception: The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

using Newtonsoft.Json;
using System;
using System.IO;
using System.Threading;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Admin.Directory.directory_v1;
using Google.Apis.Admin.DataTransfer.datatransfer_v1;
using System.Collections.Generic;
using Google.Apis.Admin.DataTransfer.datatransfer_v1.Data;

class Program
{

public class ServiceAccountJson
{
public string type { get; set; }
public string project_id { get; set; }
public string private_key_id { get; set; }
public string private_key { get; set; }
public string client_email { get; set; }
public string client_id { get; set; }
public string auth_uri { get; set; }
public string token_uri { get; set; }
public string auth_provider_x509_cert_url { get; set; }
public string client_x509_cert_url { get; set; }

    }

    static void Main(string[] args)
    {
        try
        {
            // Get ServiceAccountJson file
            string credPath = Directory.GetCurrentDirectory() + @"\HrIntegrated.json";
            var json = File.ReadAllText(credPath);
            var cr = JsonConvert.DeserializeObject<ServiceAccountJson>(json);
            ServiceAccountCredential credential = new ServiceAccountCredential(new ServiceAccountCredential.Initializer(cr.client_email.ToString())
            {
                Scopes = new[] { DirectoryService.Scope.AdminDirectoryUser,
                                 DataTransferService.Scope.AdminDatatransfer}
            }.FromPrivateKey(cr.private_key.ToString()));

 }

am I missing some thing ? Please help. Many thanks in advance.