using Newtonsoft.Json;

using System;

using System.Collections.Generic;

namespace _51817656

{

    public class Program

    {

        public static void Main(string[] args)

        {

            string jsonString = "[{\"Project\":\"example\", \"Ref\":\"001BC50C70000A21\", \"Latitude\":43.643166, \"Longitude\":1.454769, \"ParkList\": [{\"Id\":\"001BC50C70000A21P1\", \"State\":1, \"DateTime\":\"2018-02-15T08:07:18.987Z\"}, {\"Id\":\"001BC50C70000A21P2\",\"State\":1,\"DateTime\":\"2018-02-15T08:11:41.824Z\"}]}]";

            //You used [square brackets] at first, so we need to deserialize with list

            List<KMessage> kMsg = JsonConvert.DeserializeObject<List<KMessage>>(jsonString);

            foreach (Parklist item in kMsg[0].ParkList)

            {

                Console.WriteLine("Id: " + item.Id + " State: " + item.State + " DateTime: " + item.DateTime);

            }

        }

    }

    public class KMessage

    {

        public string Project { get; set; }

        public string Ref { get; set; }

        public float Latitude { get; set; }

        public float Longitude { get; set; }

        //I guess here is the problem, instead of array you can use list

        public Parklist[] ParkList { get; set; }

    }

​

    public class Parklist

    {

        public string Id { get; set; }

        public int State { get; set; }

        public DateTime DateTime { get; set; }

    }

}

​