public class PollSmsService : IHostedService, IDisposable
{
    private readonly TenantContext _context;
    private readonly IConfiguration _configuration;
    private Timer _timer;

    public PollSmsService(TenantContext context, IConfiguration configuration)
    {
        _context = context;
        _configuration = configuration;
    }

    public Task StartAsync(CancellationToken cancellationToken)
    {
        _timer = new Timer(DoWork, null, TimeSpan.Zero,
            TimeSpan.FromMinutes(1));

        return Task.CompletedTask;
    }

    private void DoWork(object state)
    {
        // Code to poll SMS status from Clickatell.
        // Not important for this example
    }

    public Task StopAsync(CancellationToken cancellationToken)
    {
        _timer?.Change(Timeout.Infinite, 0);

        return Task.CompletedTask;
    }

    public void Dispose()
    {
        _timer?.Dispose();
    }

services.AddHostedService<PollSmsService>();