title: Retrofit 2.3.0 always executing onFailure
body: <p>i'm trying to send post request using retrofit with @FormUrlEncode, here is my service class</p>
  
  <pre><code>import com.dolphithronelab.siastar.response.AuthResponse;
  
  import java.util.List;
  
  import retrofit2.Call;
  import retrofit2.http.Field;
  import retrofit2.http.FormUrlEncoded;
  import retrofit2.http.GET;
  import retrofit2.http.POST;
  
  public interface SIAStarService {
  
      @FormUrlEncoded
      @POST("auth")
      Call&lt;AuthResponse&gt;login(@Field("username") String username, @Field("password") String password);
  }
  </code></pre>
  
  <p>here is my retrofit client class</p>
  
  <pre><code>import retrofit2.Retrofit;
  import retrofit2.converter.gson.GsonConverterFactory;
  
  public class RetrofitClient {
      private static Retrofit retrofitClient =null;
      public static Retrofit getClient(String apiserver){
          if (retrofitClient == null){
              retrofitClient = new Retrofit.Builder().baseUrl(apiserver).addConverterFactory(GsonConverterFactory.create()).build();
          }
          return retrofitClient;
      }
  }
  </code></pre>
  
  <p>and here is how i communicate with the api server with ApiKomunikator class</p>
  
  <pre><code>public class ApiKomunikator {
  public static final String BASE_URL = "http://10.44.7.118/siastar/public/api/";
  public static SIAStarService getSIAStarService(){
      return RetrofitClient.getClient(BASE_URL).create(SIAStarService.class);
  }
  }
  </code></pre>
  
  <p>and here how i call from the activity</p>
  
  <pre><code>siaStarService.login(mUsernameView.getText().toString(),mPasswordView.getText().toString())
                  .enqueue(new Callback&lt;AuthResponse&gt;() {
                      @Override
                      public void onResponse(Call&lt;AuthResponse&gt; call, Response&lt;AuthResponse&gt; response) {
                          if(response.isSuccessful())
                          {}
                      }
  
                      @Override
                      public void onFailure(Call&lt;AuthResponse&gt; call, Throwable t) {
                          Toast.makeText(LoginActivity.this, "Gagal koneksi ke server, periksa jaringan internet anda error: "+t.getMessage(), Toast.LENGTH_LONG).show();
                          showProgress(false);
                      }
                  });
  </code></pre>
  
  <p>when i try to post data via postman, there is no problem, is this because i use static ip or what? and t.getMessage() always null</p>