Http request not working on android (working on ios/brower) ionic 4 angular 5

I am new to ionic, and I think I have a standard http request set up.

import { HttpClient, HttpHeaders } from ‘@angular/common/http’;

const data = {audio: audioBytes};
return new Promise(resolve => {‘http://localhost:3333/upload/’, JSON.stringify(data), {
headers: new HttpHeaders().set(‘Content-Type’, ‘application/json’)
.subscribe(data => {
}, err => {
console.log("Error: ", JSON.stringify(err));

The error I am getting is

Error”,“url”:null,“ok”:false,“name”:“HttpErrorResponse”,“message”:“Http failure response for (unknown url):
0 Unknown Error”,“error”:{“isTrusted”:true}}

I think it is because of CORS, so I set up my web server to accept CORS. And it is working on ios/browser. However, it is still getting this error on Android. Also, my web server didn’t receive any requests from Android (not even the OPTIONS request).

Any suggestion is appreciated!

I would not describe this as anywhere close to “standard”. Follow the idioms in part 6 of the Tour of Heroes instead.

Do not:

  • explicitly instantiate a Promise
  • stringify the payload
  • create custom headers
  • set content type
  • subscribe in the same place you generate the Observable, but rather return it instead
  • use localhost, because it won’t work on device


  • use HTTPS instead of naked HTTP
  • use a host name instead of localhost
  • get an SSL certificate
  • work with the Observables that HttpClient gives you

Thanks for the advice! It turned out that android cannot use localhost, but ios can.

For localhost vs host name, localhost does make development easier though.