Json.stringify not working or am doing it totaly wrong. someone help me

Am trying to create a login page

login.html

<form (ngSubmit) = "signIn()" novalidate>
					<ion-list no-line>
						<ion-item>
							<ion-label floating>Email</ion-label>
							<ion-input [(ngModel)] ="loginData.email" name="email" type="text" ></ion-input>
						</ion-item>
						<ion-item>
							<ion-label floating>Password</ion-label>
							<ion-input [(ngModel)]="loginData.password" name="password" type="password" ></ion-input>
						</ion-item>
					</ion-list>	

					<button ion-button block outline color="primary" type="submit">Sign In </button>
					
</form>

login.ts

export class Login {

  loginResponse:any;
  loginData = {"email":"","password":""};

  constructor(public navCtrl: NavController, public navParams: NavParams,public apiService: ApiService) {
  }

 signIn() {
   
    this.apiService.postData(this.loginData,'login').then((result) => {
      this.loginResponse = result;
      console.log(this.loginResponse);   
       // this.navCtrl.push(HomePage);
    }, (err) => {
        // Error message
     });

  }
}

And finaly my provider

 postData(data,key) {
    console.log('in api');
    console.log(data);
    return new Promise((resolve,reject) => {
      let headers = new Headers();     
      this.http.post(baseUrl+key,JSON.stringify(data),{headers:headers}).subscribe(res => {
        resolve(res.json());

      },(err) => {

          reject(err);

      });

    }); 

  }

This is the format am getting in my api file and it is causing errors

Object {email: “emil@gmail.com”, password: “test”}

Note that the same method actually worked for registration form

Are you certain that your backend is expecting JSON?