Problem with diagnostic

I try to get the the Bluetooth state with diagnostic in Ionic 4.12.0, but it gona someproblem here

      .then((state) => {
        if (state == this.diagnostic.bluetoothState.POWERED_ON){
        } else {
          console.log("Not Okay");

I already import with ngx append import {Diagnostic} from “@ionic-native/diagnostic/ngx”;
But when test on my android phone it show the error that Object(…) is not a function in that line this.diagnostic.getBluetoothState()