Ionic ต่อกับ API Loing เกิด Error Code 500 Server

import { Injectable } from '@angular/core';
import { Http, Headers } from '@angular/http';
import 'rxjs/add/operator/map';
let apiUrl = "http://203.150.53.203:8080/api/CMSSigninAuthenicationTest" ; 
@Injectable()
export class AuthService {
  constructor(public http: Http) {
    console.log('Hello AuthService Provider'); 
  }
  postData(credentials){
    return new Promise((resolve, reject) =>{
      let headers = new Headers();
      this.http.post(apiUrl,JSON.stringify(credentials),{headers: headers}). 
      subscribe(res =>{
        resolve(res.json());
      }, (err) =>{
        console.log(err);
       reject(err); 
      });

    });
  }
}

import { Component } from '@angular/core';
import { IonicPage, NavController } from 'ionic-angular';
import { TabsPage } from '../tabs/tabs';
import {AuthService} from "../../providers/auth-service";
@IonicPage()
@Component({
  selector: 'page-login',
  templateUrl: 'login.html',
})
export class Login {
  resposeData : any;
  userData = {"u":"", "p":"","type": 2};
  constructor(public navCtrl: NavController, public authService: AuthService) {
  }
  ionViewDidLoad() {
    console.log('ionViewDidLoad Login');
  }
  login(){
   this.authService.postData(this.userData).then((result) =>{
    this.resposeData = result;
    console.log(this.resposeData);
    localStorage.setItem('userData',JSON.stringify(this.resposeData) )
    this.navCtrl.push(TabsPage);
  }, (err) => {
      console.log(err); 
      //Connection failed message 
    });
  }

}