Ionic 5 firebasex native plugin getToken() always returns null

Ionic Framework
1

Hi,
I"m using firebasex for push notifications:

import { FirebaseX } from "@ionic-native/firebase-x/ngx";

@NgModule({
    providers: [
        FirebaseX,
    ]
})

And in the component:

constructor(private firebase: FirebaseX)

this.firebase.getToken().then(token => console.log(`The token is ${token}`))

But the token always returns null.
Any advise please?