HTTP帖子离子显示错误

Question

我已经编写了这段代码，

ServiceProvider.ts

postData() {
  return new Promise((resolve, reject) => {

    var cred = {
      "username": "abc",
      "password": "password",
      "admin_channels": "[channel_abc]"
    };
    var header = {
      headers: {
        "Content-Type": "application/json"
      }
    };

    this.http.post(apiUrl + 'api/login', cred, header).subscribe(data => {
      resolve(data);
    }, err => {
      reject(err);
    });
  });
}

通过这种方式致电服务提供商

this.authService.postData().then((result) => {
  this.loading.dismiss();

  alert("full data " + JSON.stringify(result));

}, (err) => {
  this.loading.dismiss();
  alert(JSON.stringify(err)); //SHows ERROR HERE
});

这给了我这个错误：

  

{“标头”：{“ normalizedNames”：{}，“ lazyUpdate”：null，“标头”：{}}，“状态”：0，“ statusText”：“未知错误”，“ url”：null ，“ ok”：false，“ name”：“ HttpErrorResponse”，“ message”：“ Http失败响应（未知url）：0未知错误”，“ error”：{“ isTrusted”：true}}

我在哪里弄错了？