nextjs revalidate gives error : Keys that need to be moved: revalidate

Question

I am trying to use the revalidate function. I tried to follow the code that Vercel offers, but I keep getting an error. Here is the function that I am using:

export async function getServerSideProps() {
  const client = await clientPromise;

  const db = client.db("myFirstDatabase");

  let users = await db.collection("users").find({}).toArray();
  users = JSON.parse(JSON.stringify(users));

  return {
    props: {
     users,
    },
    revalidate: 15,
  };
}

And here is the mongodb file that returns the client:

import { MongoClient } from 'mongodb'

const uri = process.env.MONGODB_URI
const options = {
  useUnifiedTopology: true,
  useNewUrlParser: true,
}

let client
let clientPromise

if (!process.env.MONGODB_URI) {
  throw new Error('Please add your Mongo URI to .env.local')
}

if (process.env.NODE_ENV === 'development') {
  // In development mode, use a global variable so that the value
  // is preserved across module reloads caused by HMR (Hot Module Replacement).
  if (!global._mongoClientPromise) {
    client = new MongoClient(uri, options)
    global._mongoClientPromise = client.connect()
  }
  clientPromise = global._mongoClientPromise
} else {
  // In production mode, it's best to not use a global variable.
  client = new MongoClient(uri, options)
  clientPromise = client.connect()
}

export default clientPromise

I have been able to connect to the database and the code works fine if I remove the revalidate part. The error that I get is :

** Error: Additional keys were returned from getServerSideProps. Properties intended for your component must be nested under the props key, e.g.:

return { props: { title: 'My Title', content: '...' } }

Keys that need to be moved: revalidate. Read more: https://nextjs.org/docs/messages/invalid-getstaticprops-value

**

I am not sure what I am doing wrong. I want to get data from the database and update it every 15 seconds. Any help would be greatly appreciated.