reference method
Implementation
Query reference(String ref) {
var url =
"https://recis-smartonbill-default-rtdb.asia-southeast1.firebasedatabase.app/";
print(ref);
var instance =
FirebaseDatabase.instanceFor(app: Firebase.app(), databaseURL: url)
.ref(ref);
return instance;
// return FirebaseDatabase.instance.ref();
// return firebaseDatabase.refFromURL(ref);
}