Firebase db listener isn't invoked when db's child is added

Question

I added the user object to firebase db in Android client, and I can see the result in firebase console.

FirebaseUser user = firebaseAuth.getCurrentUser();
DatabaseReference ref = database.getReference("users");
ref.child(user.getUid()).setValue(mUser);

In backend - node.js, firebase db reference listen 'child_added' event, But it never invoked, and I can't see any logs.

var db = firebase.database();
var ref = db.ref("users");

ref.on("child_added", function(snapshot, prevChildKey){
  console.log("child_added: " + snapshot);
});

In case of adding user in node.js server side, the listener is called.

ref.child("user1").set("user1");

I didn't set any db rules and securities. Why listener isn't called?

Answer 1

I resolved this issue after I remove the service account parameter in initializeApp of node.js side.