admin.firestore.FieldValue.serverTimestamp() not working with Firebase Realtime Database

I am trying to write a messaging application with Firebase Realtime Database, which already has some functionality on Cloud Firestore. I wrote the following code snippet in a file messages.js

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

admin.initializeApp(config);//config information

const realtime_db = admin.database();


const { uuid } = require("uuidv4");

const {
    generate_message_structure,
} = require("../util/schema");


exports.async_create_message = async function(data, context) {
    try {
        const message = generate_message_structure(data);//creates a Javascript Object

        const message_log_id = "Some_id";//derived from a function
        //Some interactions with Cloud Firestore



        const generated_token = uuid();
        await realtime_db.ref(`messages/${message_log_id}/${generated_token}`).set(message);

        console.log(message);//output shown later

        console.log("Message created");
        console.log(`message_id of ${generated_token}`)
    } catch (error) {
        console.log(error);
    }
}

I wrote my tests at the bottom of the same file, and ran node messages.js to create a record in the database.

const mockMessage = {};//capitalised constants are strings

mockMessage[MESSAGE_BODY] = "Test body";
mockMessage[MESSAGE_SENDER_ID] = "Alice_id";
mockMessage[MESSAGE_RECEIVER_ID] = "Bob_id";
mockMessage[MESSAGE_IMAGE] = {
    uid: "random_id",
    url: "google.com"
};

exports.async_create_message(mockMessage);

The output from my console.log as annotated earlier has the following structure.

{
  body: 'Test body',
  sender_id: 'Alice_id',
  receiver_id: 'Bob_id',
  image: { uid: 'random_id', url: 'google.com' },
  last_updated: ServerTimestampTransform {},
  created_at: ServerTimestampTransform {},
  seen: false
}

but when I check the record on my database, all fields are present except the last_updated and created_at timestamp fields. May I know what's wrong with this code snippet?