ulong appID = 1234567;
var email = "example@mail.ru";
var pass = "Pa$$w0rd";
var scope = Settings.Messages;
var vk = new VkApi();
vk.Authorize(new ApiAuthParams
{
ApplicationId = appID, Login = email, Password = pass, Settings = scope
});
var users = vk.Messages.GetChatUsers(29);
foreach (var user in users)
{
Console.WriteLine($"UserId: {user}");
}