How can I consume an API in ASP.NET with C#, RestSharp and display the obtained data in a DropdownList?

Question

I need help on how to fill a dropdownlist in ASP.NET with c#, with the data I get from a web API (JSON), I've tried several ways and I can't make it work.

this is my method

protected async Task LlenarDropDowndplGroupArticulosAsync()
{
    var client = new RestClient("url");
    var request = new RestRequest();
    request.AddHeader("Authorization", "Basic token");
    request.AddHeader("Content-Type", "text/plain");
    request.AddHeader("Cookie", "");
    var body = @"{
    " + "\n" +
    @"    
    " + "\n" +
    @"}";
    request.AddParameter("text/plain", body, ParameterType.RequestBody);
    RestResponse response = await client.ExecuteAsync(request);
    var Lista_desplegable = System.Text.Json.JsonSerializer.Deserialize<Lista_desplegable>(response.Content);
    ddlGroupArticulos.DataSource = Lista_desplegable;
    ddlGroupArticulos.DataTextField = "Grupo_articulo";
    ddlGroupArticulos.DataValueField = "Denominacion";
    ddlGroupArticulos.DataBind();
    ddlGroupArticulos.Items.Insert(0, new ListItem("Seleccione..", ""));
}

and this is my class

public class Lista_desplegable
{
    public string Grupo_articulo { get; set; }
    public string Denominacion { get; set; }
}