using System.Threading.Tasks;

​

public interface IMyApp

{

    Task<string> Payment();

    Task NotifyPayer(string paymentCode);

    Task NotifyReceiver(string paymentCode);

}

​

public class Program

{

    private static IMyApp ctx;

    public static async Task Main()

    {

        string paymentCode;

        int retries = 3;

        while (true)

        {

            try

            {

                paymentCode = await ctx.Payment();

                break;

            }

            catch

            {

                if (--retries == 0)

                    throw;

            }

        }

​

        ctx.NotifyPayer(paymentCode).GetAwaiter().GetResult();

        ctx.NotifyReceiver(paymentCode).GetAwaiter().GetResult();

    }

}

​

​