While sending data from my local API to MongoDB why does it saves an extra key which wasn't passed

Question

Sample Data Uploaded

{"_id":{"$oid":"63da91711b5a61ae22f2fdf1"},"title":"Tu raj kare","artist":"Jaago Music","tempo":{"$numberInt":"68"},"link":"https://www.youtube.com/watch?v=6M844pWC31M","__v":{"$numberInt":"0"}}

the last value of __v":{"$numberInt":"0"} shouldn't be there

Here is the model I am using

const mongoose = require('mongoose');

const songSchema = new mongoose.Schema({
    title: String,
    artist: String ,
    tempo: Number,
    link: String,
});

const Song = mongoose.model('songs', songSchema);

module.exports = Song;

This is the router code I am using to upload the data to MongoDB

router.post('/upload', async (req, res) => {
    const { title, artist, tempo, link } = req.body;

    if (!title || !link) {
        return res.status(422).json({ error: "Please fill all the fields" });
    }

    try {
        //FINDS IF THE SONG ALREADY EXISTS IN THE DATABASE
        const songExists = await Song.findOne({ title: title });
        if(songExists) {
            return res.status(422).json({ error: "Song already exists" });
        }
        //SAVES THE SONG TO THE DATABASE
        const song = new Song({title, artist, tempo, link});
        await song.save()
        res.status(201).json({ message: "Song uploaded successfully" });
    } catch (error) {
        console.error(error);
    }
});

I am just trying to upload Song details which contains title , artist, tempo, link.

The things getting shown in my MongoDB Atlas Collection is title , artist, tempo, link & --v

--v is unnecessary