Next.js + MongoDB: Connection is closed in double loading

Question

I tried searching a lot on the internet but I didn't find an effective solution. It turns out that, when loading two pages at the same time, one of them generates the error "MongoDB: Connection is closed", on the client side I am using getServerSideProps so that the api is called on the server side (I believed that this would solve the problem), but now I believe the problem is in the api.

I'm going to use this example API, it looks like this:

export default async function handler(req: NextApiRequest, res: NextApiResponse) {
    // Get query/params 

    try {
        const db = await getDatabase(process.env.APP_DB);
        const users = db.collection('users');
    
        const user = await users.findOne({
            refresh_token: refreshToken
        });
    
        if (!user) return res.status(403).json({ error: "Not authorized." });
    
        res.status(200).json({ name: user.name, lastname: user.lastname, email: user.email, phone: user.phone, refreshToken: user.refresh_token });

    } catch (error) {
        console.error(error);
    } finally {
        await closeDatabase()
    }
    
}

Yes, I am opening and closing my connection on each API call because I haven't seen effective ways to use the connection pool without leaking connections.

To help, I tried leaving my connection to the database as follows:

const client = new MongoClient(MONGODB_URI, {
});

let cachedDb = null;

async function connectToDatabase(dbName) {
  if (cachedDb) {
    return cachedDb;
  }

  try {
    await client.connect();
    const db = client.db(dbName);
    cachedDb = db;
    return db;
  } catch (error) {
    console.error('Error connecting to MongoDB:', error);
    throw error;
  }
}

export async function getDatabase(dbName) {
  if (!cachedDb) {
    await connectToDatabase(dbName);
  }
  return cachedDb;
}

export async function closeDatabase() {
  if (cachedDb) {
    await client.close();
    cachedDb = null;
  }
}

Note: I am ignoring imports and other irrelevant information in this example.

I'm using next14 and mongoose 8.2.0.

Unfortunately I was not successful and one connection continues to close the other halfway. Can you help me with a solution? I'm a curious, novice developer. Thanks!