discord.net The server responded with error 50001: Missing Access

I would like to retrieve users in discord guild but I get an error with cryptic message.

The server responded with error 50001: Missing Access

The bot has Administrator permission, that's what it states in Server settings > Roles > Permissions

Perhaps something else is needed to tick off in configuration.

Your thoughts?

Thanks for help.

Code

  class Program
    {
        private static IDiscordClient _client;
        private static bool _isRunning = false;
        private static Timer _timer;

        static async Task Main(string[] args)
        {
            AppDomain.CurrentDomain.ProcessExit += new EventHandler(ProcessExit);
            var client = new DiscordSocketClient(new DiscordSocketConfig()
            {
                AlwaysDownloadUsers = true,
                MessageCacheSize = 200,
            });
            var botToken = "...";

            await client.LoginAsync(TokenType.Bot, botToken);
            await client.StartAsync();
            client.Ready += Ready;
            _client = client;
            await Task.Delay(Timeout.InfiniteTimeSpan);
        }

        private static async Task Ready()
        {
            _timer = new Timer(GetUsers, null, TimeSpan.Zero, TimeSpan.FromSeconds(10));
        }

        private static async void GetUsers(object state)
        {
            if (_isRunning)
            {
                return;
            }

            _isRunning = true;

            try
            {
                var guilds = await _client.GetGuildsAsync();
                var guild = guilds.First();

                var users = await guild.GetUsersAsync();
                Console.WriteLine(users.Count);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }

            _isRunning = false;

        }

        static void ProcessExit(object sender, EventArgs e)
        {
            (_client as DiscordSocketClient).LogoutAsync().GetAwaiter().GetResult();
        }
    }

Discord Developer Portal - Scopes and bot permissions under OAuth2 configuration

Link which I used to invite bot to server.

https://discord.com/oauth2/authorize?client_id=<>&permissions=8&scope=applications.commands%20bot