Google Cloud Functions Notifications iOS

I was finishing up an app for somebody but needed some help with the script that I wrote for sending notifications via Cloud Functions for Firebase. Below this text you can find my code:

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);

exports.sendNotification = functions.database.ref('/Users/{userUid}/').onWrite(event => {
  const followerUid = event.params.userUid;

    const payload = {
      notification: {
        title: 'Update Received',
        body: 'Please Check Your App',
        badge: 1,
        sound: 1,
      }
    };

    return admin.database().ref('/Admin/notificationID').once('value').then(allTokens => {
        if (allTokens.val()) {
            // Listing all tokens.
            const tokens = allTokens.value
            return admin.messaging().sendToDevice(tokens, payload).then(response => {

        });
        };
    });  
});

Mainly there are only 3 issues that I am having. First of all, I am not sure if I am using the correct syntax for specifying the badge. Second of all, I don't know how to specify that I want a sound to be played for the notification. Lastly, I am unable to send the notification because the notificationID that is returned from the database is apparently incorrect even though I have a legible FCM ID stored in my database under /Admin/ with the key notificationID. I would appreciate it if one of you could help me fix these issues and get this app up and running.

Thanks, KPS