استفاده از Static Constructors

using Flurl.Http;
using Flurl.Http.Newtonsoft;

namespace MyCode
{
    public class ApiServiceAgent
    {
        private readonly string _baseHttpAddress;

        static ApiServiceAgent()
        {
            FlurlHttp.Clients.UseNewtonsoft();
        }

        public ApiServiceAgent(string baseHttpAddress)
        {
            _baseHttpAddress = baseHttpAddress;
        }

        public async Task<TResponse> SendAsHttpPostAsync<TResponse, TInput>(TInput message, string url, Dictionary<string, string> headers = null)
        {
            throw new Exception(error, ex); 
        }
    }
}