Http post does not work


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, body, options)

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

URL must be blank, or is in wrong format