APP_ID = "rbX1M9zOybz1xmFis05dWxtT-gzGzoHsz";
[HttpPost]
[AllowAnonymous]
public async Task SendSmsCode(string mobilePhone)
{
if (string.IsNullOrEmpty(mobilePhone))
{
return Json(new ResultEntity() { SUCCESS = false, DESC = "请填写手机号码" });
}

        var httpClient = new HttpClient();
        var uri = new Uri("https://api.leancloud.cn/1.1/requestSmsCode");

        httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("*/*"));
        httpClient.DefaultRequestHeaders.Add("X-LC-Id", APP_ID);
        httpClient.DefaultRequestHeaders.Add("X-LC-Key", APP_KEY);

        var content = new StringContent("{\"mobilePhoneNumber\":\"" + mobilePhone + "\"}", Encoding.UTF8, "application/json");
        content.Headers.ContentType = new MediaTypeHeaderValue("application/json");

        try
        {
            bool success = false;

            using (var response = await httpClient.PostAsync(uri, content))
            {
                success = response.IsSuccessStatusCode;
            }

            return Json(new ResultEntity<bool>() { SUCCESS = success, DESC = success ? "已发送" : "发送短信失败" });
        }
        catch (Exception ex)
        {
            MyLog4NetInfo.ErrorInfo(ex.Message);
            return Json(new ResultEntity<bool>() { SUCCESS = false, DESC = "发送短信失败" });
        }
        finally
        {
            httpClient.Dispose();
        }
    }

response
{StatusCode: 400, ReasonPhrase: 'Bad Request', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-store, no-cache
Date: Wed, 11 May 2016 01:01:55 GMT
Server: Tengine
Content-Length: 62
Content-Type: application/json; charset=utf-8
}}
Content: {System.Net.Http.StreamContent}
Headers: {Connection: keep-alive
Pragma: no-cache
Cache-Control: no-store, no-cache
Date: Wed, 11 May 2016 01:01:55 GMT
Server: Tengine
}
IsSuccessStatusCode: false
ReasonPhrase: "Bad Request"
RequestMessage: {Method: POST, RequestUri: 'https://api.leancloud.cn/1.1/requestSmsCode', Version: 1.1, Content: System.Net.Http.StringContent, Headers:
{
Accept: /
X-LC-Id: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
X-LC-Key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Content-Type: application/json
Content-Length: 35
}}
StatusCode: BadRequest
Version: {1.1}

好的，我试下

不行，一样的结果。
response
{StatusCode: 400, ReasonPhrase: 'Bad Request', Version: 1.1, Content: System.Net.Http.StreamContent, Headers:
{
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-store, no-cache
Date: Wed, 11 May 2016 01:16:12 GMT
Server: Tengine
Content-Length: 44
Content-Type: application/json; charset=utf-8
}}
Content: {System.Net.Http.StreamContent}
Headers: {Connection: keep-alive
Pragma: no-cache
Cache-Control: no-store, no-cache
Date: Wed, 11 May 2016 01:16:12 GMT
Server: Tengine
}
IsSuccessStatusCode: false
ReasonPhrase: "Bad Request"
RequestMessage: {Method: POST, RequestUri: 'https://api.leancloud.cn/1.1/requestSmsCode', Version: 1.1, Content: System.Net.Http.StringContent, Headers:
{
Accept: /
X-LC-Id: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
X-LC-Key: XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
Content-Type: application/json
Content-Length: 35
}}
StatusCode: BadRequest
Version: {1.1}

相同的代码，什么都没动，
2016-05-09 18:56:49 之前还是好的，
在这个时间点之后应该是服务端有什么调导致的验证失败。

这是Dot Net格式的数据，content对象的成员的数据无法打印出来。
可以确定的是这段时间我们没有发布新的程序，
验证从可用变成了不可用，
应该是你们服务端做了修改的。

你们有没有C#调用服务端接口的官方示例代码？