using System;

using System.Collections.Generic;

using Newtonsoft.Json;

using Newtonsoft.Json.Converters;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var json = "{\"createdDate\":\"20200501\"}";

​

        var account = JsonConvert.DeserializeObject<Account>(json);

        Console.WriteLine(account.CreatedDate);

    }

}

​

public class CustomDateTimeConverter : IsoDateTimeConverter

{

    public CustomDateTimeConverter() => DateTimeFormat = "yyyyMMdd";

}

public class Account

{

    [JsonConverter(typeof(CustomDateTimeConverter))]

    public DateTime? CreatedDate { get; set; }

}

​