Cloud Function executed successfully but notification not showing android

In an android app, I am using FCM for sending notifications, the cloud function executed successfully, as shown in the firebase console log, but in my device its not showing any notification, what could be the reason ?

Below is the code for my index.js

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

exports.sendNotification = functions.database.ref('/notifications/messages/{pushId}')
.onWrite(event => {
     console.log('notifying start1');
    const message = event.data.current.val();
    const senderUid = message.from;
    const receiverUid = message.to;
    console.log('SenderId '+senderUid + ' Receiver Id '+receiverUid);
    const promises = [];
 console.log('notifying start2');
    if (senderUid == receiverUid) {
        //if sender is receiver, don't send notification
        promises.push(event.data.current.ref.remove());
        return Promise.all(promises);
    }
      console.log('notifying start3');
    const getInstanceIdPromise = admin.database().ref(`/users/${receiverUid}/accessToken`).once('value');
      console.log('notifying start4');
    const getReceiverUidPromise = admin.auth().getUser(receiverUid);
console.log('notifying start5');
    return Promise.all([getInstanceIdPromise, getReceiverUidPromise]).then(results => {
        const accessToken = results[0].val();
        const receiver = results[1];
        console.log('notifying ' + receiverUid + ' about ' + message.body + ' from ' + senderUid);
        const payload = {
            notification: {
                title: 'Firebase Notification',
                body: message.body,
            }
        };
        admin.messaging().sendToDevice(accessToken, payload)
            .then(function (response) {
                console.log("Successfully sent message:", response);
            })
            .catch(function (error) {
                console.log("Error sending message:", error);
            });   
            });
            });

Kindly help! Thanks in advance.