public class MyBackgroundService : BackgroundService
{
    private readonly ICustomService _service;
    private IProgress<JSONMessage> _progress;

    public MyBackgroundService(ICustomService service)
    {
        _service = service;
        _progress = new Progress<JSONMessage>();
        _progress.ProgressChagned += Progress_Changed;
    {

    protected override async Task ExecuteAsync(CancellationToken cancellationToken)
    {
        await _service.StartService(_progress);

        while (!cancellationToken.IsCancellationRequested)
        {
            await Task.Delay(TimeSpan.FromSeconds(1), cancellationToken);
        }
    }

    private void Progress_Changed(object s, JSONMessage e)
    {
        Console.WriteLine(e.Id);
    }
}