带参数错误的C＃PostAsync

Question

我在下面编写代码来调用第三方API但返回错误：参数错误。我在Postman中测试它可以返回响应JSON结果。任何人都可以帮助我做错了。

namespace DemoApps
{
    class Program
    {
        static HttpClient httpClient = new HttpClient();

        class P
        {
            public string language_id { get; set; }

            public string order_no { get; set; }

            public string token { get; set; }
        }

        static void Main(string[] args)
        {
            string url = "http://medpro.vizzhost.com/linsy/eshop/admin/index.php?route=api/order/getByNo";

            string paramStr = Newtonsoft.Json.JsonConvert.SerializeObject(new P() {
                language_id = "1",
                order_no = "1707170018",
                token = "6b887489372f483792d490f5bc8104ef"
            });

            HttpContent content = new StringContent(paramStr, System.Text.Encoding.UTF8);
            content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
            var response = httpClient.PostAsync(url, content)
                .Result.Content.ReadAsStringAsync();

            Console.WriteLine(response.Result.ToString());
            Console.ReadKey();

        }
    }
}

Program return error

Postman running result