Http post does not work

Ionic Framework ionic-v3
1

Hi,

I always get an error unkown host in error message from ios simulator or from ios device.

 public login(username: string, passwd: string): Observable<string> {
    const headers = new HttpHeaders({'Content-Type': 'application/x-www-form-urlencoded'});
    const options = {headers: headers, withCredentials: true};
    const body = {
      'username': username,
      'password': passwd
    };
    return this.http.post(URL, body, options)
      .map(xxx)
      .catch(xxx);
  }

In catch block I got the message "Http failure response for (unkown url).
Does anybody have any idea?
I build with ionic cordova build ios --release

2

URL must be blank, or is in wrong format