SecureStorage not installed, but it is in Ionic3 - ionic-framework

Question

I am migrating Storage to SecureStorage. The normal storage worked fine, but I have problems with secure storage on all platforms.
I installed the plugin like here described. But if I run the app in the browser or on Android, I get following errors:
plugin_not_installed
(...)
ERROR Error: "Uncaught (in promise): TypeError: this.storage is undefined
[42]/DataProvider.prototype.getLoginData
I imported SecureStorage as Provider into app.module.ts.
app.component.ts looks like this:
constructor(public platform: Platform, public statusBar: StatusBar, public splashScreen: SplashScreen, private dataProvider: DataProvider, private restProvider: RestProvider) {
this.initializeApp();
// ...
}
initializeApp() {
this.platform.ready().then(() => {
this.statusBar.styleDefault();
this.dataProvider.getLoginData().then((loginData) => {
console.log(loginData);
}, (error) => {
console.error(error);
});
}
And DataProvider looks like this:
import {Injectable} from '#angular/core';
import {SecureStorage, SecureStorageObject} from '#ionic-native/secure-storage';
/**
* #see https://ionicframework.com/docs/native/secure-storage/
* #see https://github.com/Crypho/cordova-plugin-secure-storage
*/
#Injectable()
export class DataProvider {
storage: SecureStorageObject;
constructor(private secureStorage: SecureStorage) {
this.secureStorage.create('com.mydomain.myapp').then((storage: SecureStorageObject) => {
DevProvider.logDebugMsg('secureStorage created');
this.storage = storage;
}, (error) => {
console.error('creating secureStorage failed: ', error); // output is: plugin_not_installed
});
}
getLoginData() {
return this.storage.get('loginData');
}
}
What's wrong here?
Thanks.