C# Post数据格式错误

[LifeCycling]

static async Task PostData(string url="https://leancloud.cn/1.1/rtm/messages"){
using(HttpClient client=new HttpClient()){
client.DefaultRequestHeaders.Add("X-LC-Id", "8998989889-gzGzoHsz");
client.DefaultRequestHeaders.Add("X-LC-Key", "898098,master");
client.DefaultRequestHeaders.TryAddWithoutValidation("Content-Type", "application/json; charset=utf-8");
//client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
var content = new FormUrlEncodedContent(new Dictionary()
{
{"from_peer", "568cb66400b009a331c556d5"},
{"message", "helloworld-099898"},
{"conv_id", "568cb67b9accde5e1980ab2d"},
{"transient", "false"}
});

	Uri serviceReq = new Uri(url); 
	await client.PostAsync(serviceReq,content).ContinueWith((requestTask)=>{
		HttpResponseMessage response=requestTask.Result;
		response.Content.ReadAsStringAsync().ContinueWith((readTask)=>{
			Console.WriteLine(readTask.Result);
		});
	});
}

}

报错提示:{"code":1,"error":"请提供 from_peer。"}
请问如何解决，谢谢

[LifeCycling]

var sr=JsonConvert.SerializeObject(ut);
StringContent theContent = new StringContent(sr, System.Text.Encoding.UTF8, "application/json");

[WuJun]

        using (HttpClient client = new HttpClient())
        {
            client.BaseAddress = new Uri("https://leancloud.cn");

            client.DefaultRequestHeaders.Add("X-LC-Id", "wdpwqs2fgowyona46ecy4luh4mn0x5obl827sjrrlj8w2vqo");
            client.DefaultRequestHeaders.Add("X-LC-Key", "6m6ky913ymaku60fqug0ieu4xh1ky2u6519olnk2obnogdlr");

            var content = new StringContent("{\"mobilePhoneNumber\": \"18612438929\"}",Encoding.UTF8, "application/json");
            var result = await client.PostAsync("/1.1/requestSmsCode", content);
          
            string resultContent = await result.Content.ReadAsStringAsync();
          
            return resultContent;

        }

[WuJun]

请参照我上面给出的结构发送 HTTP 请求。
这个是发送短信的，你那边的需求就是改成发送消息的。