Ionic3 Fileopener plugin Object(…) is not a function Error

Question

I installed FileOpener plugn for Ionic

The project is being compiled and build succesffuly, but when calling the plugin's open function it throws Object(…) is not a function error.

Full Error stacktrace:

"TypeError: Object(...) is not a function
    at FileOpener.open (file:///android_asset/www/build/vendor.js:101646:143)
    at file:///android_asset/www/build/8.js:324:34
    at t.invoke (file:///android_asset/www/build/polyfills.js:3:14976)
    at Object.onInvoke (file:///android_asset/www/build/vendor.js:4982:33)
    at t.invoke (file:///android_asset/www/build/polyfills.js:3:14916)
    at r.run (file:///android_asset/www/build/polyfills.js:3:10143)
    at file:///android_asset/www/build/polyfills.js:3:20242
    at t.invokeTask (file:///android_asset/www/build/polyfills.js:3:15660)
    at Object.onInvokeTask (file:///android_asset/www/build/vendor.js:4973:33)
    at t.invokeTask (file:///android_asset/www/build/polyfills.js:3:15581)"

Plugin's declaration on app.module and in the component:

import { FileOpener } from '@ionic-native/file-opener/ngx';

plugin usage:

 this.fileOpener.open(uri, 'application/pdf')
    .then(() => {
      console.log('File is opened');
      loading.dismiss();}
      ).
      catch(err =>  {
        debugger;
          console.error('Error openening file: ' + err);
          loading.dismiss();}
        );

Ionic info:

  ionic (Ionic CLI)  : 4.1.2
  Ionic Framework    : ionic-angular 3.9.2
  @ionic/app-scripts : not installed

What could possibly cause this error?

Thanks