How to write a new key to every existing UID with Firebase Functions

Question

I am trying to write a new key to every existing UID when a new notification sent.

The code works like this; When a new message is written to realtime database a new notification is sent to every device.

So far it works in my code.

But I want to write to the existing UID's, a new entry for notification count badge in my android app to show unread count.

EDIT: Problem is solved. See next code block.

Here is my code:

import * as functions from 'firebase-functions';

const admin = require("firebase-admin");
admin.initializeApp();

/** NOTIFICATIONS */


exports.sendNotification = functions.database.ref('/notifications/{pushId}')
    .onCreate((snapshot, context) => {

        const notification = snapshot.val();
        const title = notification.title;


        const topic = 'notifications';

        const message = {
            data: {
                title: notification.title,
                body: notification.message,
                link: notification.link,
            },
            topic: topic
        };


        // Send a message to devices subscribed to the provided topic.
        admin.messaging().send(message)
            .then((response: String) => {
                // Response is a message ID string.
                console.log('Successfully sent message: ', response);
                writeBadge()

            })
            .catch((error: String) => {
                console.log('Error sending message: ', error);
            });



        return null;
    });

    // The problem is in this function

function writeBadge() {


    return admin.database().ref('/users').once('value').then(function (snapshot) {

        snapshot.forEach((userSnapshot => {
            const uid = userSnapshot.key;

            const myRef = admin.database().ref("/users/" + uid + "/badge").push();
            const key = myRef.key;
            userSnapshot.child("badge/" + key).set({
                key: true
            });

            console.log('Pushed UID: ' + uid);


        }));

    });
}

This is the answer I was looking. This works for me.

function writeBadge() {


    return admin.database().ref('/users').once('value').then(function (snapshot) {

        snapshot.forEach((userSnapshot => {
            const uid = userSnapshot.key;

            const myRef = admin.database().ref("/users/" + uid + "/badge").push();

            myRef.set({
                key: true
            });

            console.log('Pushed UID: ' + uid);


        }));

    });
}