The specified content type was not found - Error 611 - NativeScript - nativescript

Question

I'm following the step by step tutorial of NativeScript but I'm facing the following issue:
When I try to make a post request through my Angular service I get the following error:
JS: {"message":"The specified content type was not found.","errorCode":611}
My code looks pretty much the same as the one in the official docs from NativeScript:
import { Injectable } from '#angular/core';
import { Http, Headers, Response } from '#angular/http';
import { User } from './user';
import { Config } from '../config';
import { Observable } from 'rxjs/Rx';
import 'rxjs/add/operator/do';
import 'rxjs/add/operator/map';
#Injectable()
export class UserService {
constructor(private _http: Http) { }
register(user: User): Observable<Response> {
const headers = new Headers();
headers.append('Content-Type', 'application/json');
const url = `${Config.apiUrl}/Users`;
const body = JSON.stringify({
Username: user.email,
Email: user.email,
Password: user.password
});
return this._http.post(url, body, { headers })
.catch(this.handleErrors);
}
handleErrors(error: Response) {
console.error(JSON.stringify(error.json()));
return Observable.throw(error);
}
}
Component class:
signUp() {
this._user.register(this.user).subscribe(
() => {
alert('Your account has been successfully created.');
this.toggleDisplay();
},
() => {
// errors here...
alert('Unfortunately we were unable to create your account.');
}
);
}
Tested under Android and IOs, both throws the same error.
Isn't application/json the expected Content-Type in this case?
If I change the type I get another error saying that the type is missing or is invalid.
Can someone please point out what am I missing?