Notification Trickered Firebase Database Query

const functions = require('firebase-functions');
const admin = require('firebase-admin');

admin.initializeApp(functions.config().firebase);


 exports.sendToATokenedDevice = functions.database.ref('/userReceiverList/{email}/{msgId}/')
     .onCreate((snapshot, context) => {
       // Grab the current value of what was written to the Realtime Database.
            console.log(`Database Trickered OnCreate Sending Notification ${context.params.email}`);
             return admin.database().ref(`/users/${context.params.email}/firebaseToken`).once('value')
                      .then(snapshot2 => {
                                            var token_device=snapshot2.val();
                                            console.log('Token',token_device);

                                            var payload = {notification : {
                                                           body : "มีวัตถุต้องสงสัย โปรดคลิกเพื่อเปิดแอพ",
                                                           title : "แอบดูค้นพบ"
                                                          },
                                                          token: token_device
                                                          };
                                           return admin.messaging().send(payload);
                     })
                     .then((response) => {
                                          // Response is a message ID string.
                                          console.log('Successfully sent message:', response);
                                          return null;
                     }).catch((error) => {
                                          console.log('Error sending message:', error);
                     });
        });