.Net Core 3.0 object Type set value

I'm trying to build my .net core 3.0 web api project but stuck on a statement last 4 days.
Here is my problem. I have a filtration model called "GridFilter" this model looks like this :

    public class GridFilter
    {
         public string Operator { get; set; }
         public string Field { get; set; }
         public object Value { get; set; }
         public object Value2 { get; set; }
         public string Logic { get; set; }
    }

in this model i keep Value and Value2 as object before filtering any model im converting this values to related column type via Universal Type Converter. I used this system in .netfreamwork working pretty well. But in .net core 3.0 when i did a request this model filling like this :
Model

Operator: "eq"
Logic: null
Value: ValueKind = Number : "10000"
Value2: null
Field: "SCT_CATEGORY"

request:
{"filter": {"filters": [{"field": "SCT_CATEGORY", "value": 10000, "operator": "eq"}]}}

I searched straight 4 days and can't fix this. Im trying to fill it like this:

Operator: "eq"
Logic: null
Value: 10000
Value2: null
Field: "SCT_CATEGORY"

How can i fix this problem.
Thanks!

EDIT

  [Route("[action]")]
    [HttpPost]
    public async Task<Response> List([FromBody]GridFilter request)

My ConfigureServices like this:

services.AddControllers()
                .AddJsonOptions(o =>
                {
                    o.JsonSerializerOptions.PropertyNamingPolicy = null;
                    o.JsonSerializerOptions.DictionaryKeyPolicy = null;
                });

and in this snippet im building my filter for fluent nhibarte

  internal static MyCriteria BuildFilter(ISession sess, GridFilter gf)
    {
        MyCriteria mc = null;
        var t = !string.IsNullOrEmpty(gf.Field)
            ? TypeHelper.GetType(typeof(T).GetProperty(gf.Field))
            : null;

        if (t == typeof(char) && (!new[] { "eq", "neq" }.Contains(gf.Operator)))
        {
            gf.Operator = "eq";
        }

        switch (gf.Operator)
        {
            case "eq":
                mc = gf.Value == null ? new MyCriteria { cr = Restrictions.IsNotNull(gf.Field), logic = gf.Logic.ToEnum(Logic.and) } : new MyCriteria { cr = Restrictions.Eq(gf.Field, ChangeType(gf.Value, t)), logic = gf.Logic.ToEnum(Logic.and) };
                break;...

And my change type methed like this:

internal static object ChangeType(object value, Type conversionType)
        {
            try
            {
                object result;
                UniversalTypeConverter.TryConvert(value, conversionType, out result);
                return result;
            }
            catch (Exception)
            {
                return false;
            }
        }

at this point i need to convert "10000" not ValueKind = Number : "10000"

As was said in one of the comments, this is change in behavior is due to .NET Core 3.0 replacing it's Json serialization engine from Newtonsoft to System.Text.Json .

I see two options for you:

First is to change the default Json serializer back to Newtonsoft. Details on how to do it are here : https://stackoverflow.com/questions/55666826/where-did-imvcbuilder-addjsonoptions-go-in-net-core-3-0/55666898#55666898

Second option is to write your own custom converter. I can imagine this converter trying to parse all known types, grabbing first that succeeds. Eg. Int.TryParse, DateTime.TryParse, etc..

Hard so say much without your deserialize code, but: this works fine:

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;

static class Program
{
    static void Main()
    {
        var request = @"{""filter"": {""filters"": [{""field"": ""SCT_CATEGORY"", ""value"": 10000, ""operator"": ""eq""}]}}";
        var obj = JsonConvert.DeserializeObject<Request>(request);
        var filter = obj.Filter.Filters.Single();
        Console.WriteLine(filter.Operator); // "eq"
        Console.WriteLine(filter.Logic); // null
        Console.WriteLine(filter.Value); // 10000
        Console.WriteLine(filter.Value2); // null
        Console.WriteLine(filter.Field); // SET_CATEGORY
    }
}
public class Request // just to shape the json
{
    public RequestFilters Filter { get; set; }
}
public class RequestFilters // just to shape the json
{
    public List<GridFilter> Filters { get; } = new List<GridFilter>();
}
public class GridFilter
{
    public string Operator { get; set; }
    public string Field { get; set; }
    public object Value { get; set; }
    public object Value2 { get; set; }
    public string Logic { get; set; }
}

If you also want to be able to serialize retaining the case, you'd need to tell the serializer:

public class Request // just to shape the json
{
    [JsonProperty("filter")]
    public RequestFilters Filter { get; set; }
}
public class RequestFilters // just to shape the json
{
    [JsonProperty("filters")]
    public List<GridFilter> Filters { get; } = new List<GridFilter>();
}
public class GridFilter
{
    [JsonProperty("operator")]
    public string Operator { get; set; }
    [JsonProperty("field")]
    public string Field { get; set; }
    [JsonProperty("value")]
    public object Value { get; set; }
    [JsonProperty("value2")]
    public object Value2 { get; set; }
    [JsonProperty("logic")]
    public string Logic { get; set; }
}