"Could not connect to the server" when @ionic-native/http post request

I'm using "@ionic-native/http": "^5.36.0" plugin for payment gateway post request call as per follows.

let nativeCall = this.httpNative.post('url', {
  'name': 'xyz',
  'password': 'zyx',
  'mode': 'authprev'
}, { 'Content-Type': 'application/x-www-form-urlencoded' });
return from(nativeCall);

Mostly getting issues on iPhone devices, sometimes it works sometimes it's not. When we call that post request getting "Could not connect to the server" error. Can you please let me know what's wrong with my code.