Using a delegate to handle a Javascript callback in JINT

Question

In the following code using JINT, the call to the Setup1 method works and the call to Setup2 method does not. The call to Setup2 raises the error: Jint.Runtime.JavaScriptException: 'No public methods with the specified arguments were found.'

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp4
{
    public delegate bool DoFunction();

    public class TestClass
    {
        public TestClass() { }

        public void Setup1(Func<bool> fn)
        {
            bool b = fn();
        }

        public void Setup2(DoFunction fn)
        {
            bool b = fn();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Jint.Engine _engine = new Jint.Engine();
            _engine.SetValue("test", new TestClass());
            _engine.Execute("test.Setup1(function() { return true; })");
            _engine.Execute("test.Setup2(function() { return true; })");
        }
    }
}

So why does the call to Setup2 fail? What is the different between Func and the delegate DoFunction()?