Why error occurred while parsing function triggers to the firebase?

Question

Hello guys i successfully set push notification by changing of realtime database.For this i used below function to get notification when app is in background. But the problem is whenever notification is arrived there is no sound will play. So i add the sound :"default" according to this question https://stackoverflow.com/questions/37959588/no-notification-sound-when-sending-notification-from-firebase-in-android

Here is my error image enter image description here Here is my function

'use strict'
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification = functions.database.ref('/Notifications/{receiver_user_id}/{notification_id}')
.onWrite((data, context) =>
{
 const receiver_user_id = context.params.receiver_user_id;
 const notification_id = context.params.notification_id;
 console.log('We have a notification to send to :' , receiver_user_id);
 if (!data.after.val()) 
 {
 console.log('A notification has been deleted :' , notification_id);
 return null;
 }
 const DeviceToken = admin.database().ref(`/Users/${receiver_user_id}/device_token`).once('value');
 return DeviceToken.then(result => 
 {
 const token_id = result.val();
 const payload = 
 {
 notification:
 {
 title: "New Chat Request",
 body: `you have a new Chat Request, Please Check.`,
 icon: "default"
 sound: "default"... ***added for default sound***
 }
 };
 return admin.messaging().sendToDevice(token_id, payload)
 .then(response => 
 {
 console.log('This was a notification feature.');
 });
 });
});

• MauriceNino: You are missing a , in the line before sound: ....
• MauriceNino: Also I am pretty sure this is just for StackOverflow, but just in case: Remove ... ***added for default sound*** too or replace it with a comment like: // ... ***added for default sound***.
• MauriceNino: Also, I am not sure, but your Promise handling does not look very ... Promising. (I'll find myself out)
• MauriceNino: icon: "default", sound: "default" You need to put a , in between those, otherwise it wont know that it is a new property. In JavaScript it is best practice to use ' ' over " ".
• Vora: still sound is not playing while notifi