I am stuck at the end to find code for
(Send a Request with LIST & Parameters to a restAPI Post with Json in WinForm C#)

i have local Web Server with WEB Api POST Method
with sending Parameters, the address is : https://localhost:44328/api/hitung

with Postman application
i send Request Parameters like this POST > Body > RAW > JSON
and have some Return Response, from with this 4 Parameters,

{
    "retailercode": "CJF00055",
    "orderitems": [
        {
            "rownumber": 1,
            "productcode": "100535",
            "qty": 5
        }
    ]
}

And in the Postman will return Response like this =

{
    "retailercode": "CJF00055",
    "orderitems": [
        {
            "rownumber": 1,
            "productcode": "100535",
            "qty": 5.0,
            "orderprice": 8727.0,
            "percentdisc": "D1.5",
            "disreg": 1.5,
            "valuediscreg": 654.525,
            "totaldisc": 654.525
        }
    ]
}

what i have tried to code :
but still get Error from my Massage Box (“Message”: “An error has occurred.”)
the problem is i dont know how to create (Parameters List Request) in my code C#
Please can someone try to help me to solved my problem?

my model List Class

public class Root0
 {
     public string retailercode { get; set; }              
     public List<orderitem0> orderitems { get; set; }
 }

 public class orderitem0
 {
    public int rownumber { get; set; }
    public string productcode { get; set; } 
    public decimal qty { get; set; }

    public decimal orderprice { get; set; }
    public string percentdisc { get; set; }      
    public decimal disreg { get; set; }          
    public decimal valuediscreg { get; set; }
    public decimal totaldisc { get; set; }  

my code have some Error.

using System;
using System.Threading.Tasks;
using System.Net.Http;
using System.Text;
using System.Text.Json;
using System.Windows.Forms;

 public async void coba5()
 {

     try
     {
         string url = "https://localhost:44328/api/hitung";
         System.Net.Http.HttpClient client = new System.Net.Http.HttpClient();

         var requestData = new Root0 @"{""RetailerCode"" : ""CJF00055"", 
                         ""orderitems"": [
                         { 
                         ""rownumber"": 1,
                         ""productcode"": ""100535"",
                         ""qty"": 5
                         }]}";

         string json = JsonSerializer.Serialize(requestData);
         var content = new StringContent(json, Encoding.UTF32, "application/json");
         var response = await client.PostAsync(url, content);
         string responseContent = await response.Content.ReadAsStringAsync();
         MessageBox.Show(responseContent);
     }
     catch (Exception ex)
     {
         MessageBox.Show(ex.Message);
     }
  }


  private void button2_Click(object sender, EventArgs e)
  {

      coba5();
  }