Restsharp Collective Query

Question

There are 500 pieces of data I got from excel in Listbox1. How can I post them all with Restsharp. In one sentence I have to put commas in the code in order for the item in listbox1. Example: ("hes" + "code"), ("hes" + "code"), ("hes" + "code"), ("hes" + "code"), ("hes" + "code" ), ....

Code :

public string hes; public string code;

    public AnaForm()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        var client = new RestClient("url);
        client.Timeout = -1;
        var request = new RestRequest(Method.POST);
        request.AddHeader("Authorization", "Basic idpw");
        request.AddHeader("Content-Type", "application/json");
        request.AddHeader("Cookie", "Cookie_1=value; mycode");

         for (int i = 0; i < listBox1.Items.Count; i++)
         {

                 if ((i + 1) <= listBox1.Items.Count )
                 {
                     hes = "hes_code";
                     code += listBox1.Items[i];
                     request.AddParameter("application/json", "[{\"" + hes + "\": \"" + code + "\"}]", ParameterType.RequestBody);
                 }
          }

        IRestResponse response = client.Execute(request);
        textBox1.Text = response.Content;