Failure Email to 535: 5.7.8 Username and Password not accepted

I'm trying to use Smtp email sender to send email for testing purpose. But getting error:

Failure Email to 535: 5.7.8 Username and Password not accepted

Following are the code:

using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.AspNetCore.Identity.UI.Services;
using SampleApi.Models.AppSettings;
using SampleApi.Models;
using MimeKit;
using MailKit.Net.Smtp;

namespace SampleApi.Bal
{
    public class EmailSender : IEmailSender
    {
        private readonly ILogger _logger;
        private readonly AuthMessageSenderOptions _authMessageSenderOptions;
        private readonly MailAppSettings _mailAppSettings;
        public EmailSender(IOptions<AuthMessageSenderOptions> optionsAccessor,
                           ILogger<EmailSender> logger,
                           IOptions<MailAppSettings> mailAppSettings)
        {
            _authMessageSenderOptions = optionsAccessor.Value;
            _logger = logger;
            _mailAppSettings = mailAppSettings.Value;
        }

        public async Task SendEmailAsync(string toEmail, string subject, string message)
        {
            await SendSMTPMailAsync(new MailData()
            {
                EmailBody = message,
                EmailSubject = subject,
                EmailToId = toEmail
            });
        }

        public async Task<bool> SendSMTPMailAsync(MailData mailData)
        {
            try
            {

                using (MimeMessage emailMessage = new MimeMessage())
                {
                    MailboxAddress emailFrom = new MailboxAddress(_mailAppSettings.SenderName, _mailAppSettings.SenderEmail);
                    emailMessage.From.Add(emailFrom);
                    MailboxAddress emailTo = new MailboxAddress(mailData.EmailToName, mailData.EmailToId);
                    emailMessage.To.Add(emailTo);

                    // you can add the CCs and BCCs here.
                    //emailMessage.Cc.Add(new MailboxAddress("Cc Receiver", "cc@example.com"));
                    //emailMessage.Bcc.Add(new MailboxAddress("Bcc Receiver", "bcc@example.com"));

                    emailMessage.Subject = mailData.EmailSubject;

                    BodyBuilder emailBodyBuilder = new BodyBuilder();
                    emailBodyBuilder.TextBody = mailData.EmailBody;

                    emailMessage.Body = emailBodyBuilder.ToMessageBody();

                    //this is the SmtpClient from the Mailkit.Net.Smtp namespace, not the System.Net.Mail one
                    using (SmtpClient mailClient = new SmtpClient())
                    {
                        await mailClient.ConnectAsync(_mailAppSettings.Server, _mailAppSettings.Port);
                        await mailClient.AuthenticateAsync(_mailAppSettings.UserName, _mailAppSettings.Password);
                        await mailClient.SendAsync(emailMessage);
                        await mailClient.DisconnectAsync(true);

                    }
                }
            }
            catch (Exception ex)
            {

                _logger.LogInformation($"Failure Email to {ex.Message}");
            }

            return true;
        }
    }
}

in appsettings:

  "MailAppSettings": {
    "Server": "smtp.gmail.com",
    "Port": 587,
    "SenderName": "",
    "SenderEmail": "",
    "UserName": "",
    "Password": ""
  }

For security reason credential field kept blank here:^.