How could push a new record into multi leveled document in mongodb

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MongoDB

Node.js

I have following document in mongoDB.

{
    "_id": {
        "$oid": "5fcca00b7bb43918340afb29"
    },
    "userEmail": "sairam0730@gmai.com",
    "ledgerID": 5,
    "ledgerName": "Direct expenses",
    "child": [{
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fcca00b7bb43918340afb2a"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",
        "childID": 4,
        "childName": "Labour charges & wages",
        "reference": "Daily wages",
        "gstApplicable": false,
        "transactions": [{
            "_id": {
                "$oid": "5fccbcba9dd51d1794a94ebc"
            },
            "transactionID": "5fccbcba9dd51d1794a94eb9",
            "date": "06-Dec-2020",
            "particulars": "To Cash",
            "voucherType": "Cash",
            "voucherNumber": "CV-3",
            "credit": 0,
            "debit": 3000
        }]
    }, {
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fcca0307bb43918340afb2b"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",

        "childID": 6,
        "childName": "Salaries",
        "reference": "Office salaries",
        "gstApplicable": false,
        "transactions": []
    }, {
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fccad64032f8924dc2cc5c3"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",
        "childID": 6,
        "childName": "Salaries",
        "reference": "Corp",
        "gstApplicable": false,
        "transactions": []
    }],
    "__v": 0
}

I need to push a transaction into transction array of a particular _id inside child object.

Like this,

{
    "_id": {
        "$oid": "5fcca00b7bb43918340afb29"
    },
    "userEmail": "sairam0730@gmai.com",
    "ledgerID": 5,
    "ledgerName": "Direct expenses",
    "child": [{
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fcca00b7bb43918340afb2a"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",
        "childID": 4,
        "childName": "Labour charges & wages",
        "reference": "Daily wages",
        "gstApplicable": false,
        "transactions": [{
            "_id": {
                "$oid": "5fccbcba9dd51d1794a94ebc"
            },
            "transactionID": "5fccbcba9dd51d1794a94eb9",
            "date": "06-Dec-2020",
            "particulars": "To Cash",
            "voucherType": "Cash",
            "voucherNumber": "CV-3",
            "credit": 0,
            "debit": 3000
        }]
    }, {
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fcca0307bb43918340afb2b"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",

        "childID": 6,
        "childName": "Salaries",
        "reference": "Office salaries",
        "gstApplicable": false,
        "transactions": [
          {
                    transactionID: "101",
                    date: "",
                    particulars: "To ",
                    voucherType: "Payments",
                    voucherNumber: "",
                    debit: 30,
                    credit: "" //Amount
                }
        ]
    }, {
        "rateOfDuty": 0,
        "openingBalance": 0,
        "closingBalance": 0,
        "_id": {
            "$oid": "5fccad64032f8924dc2cc5c3"
        },
        "ledgerID": 5,
        "ledgerName": "Direct expenses",
        "childID": 6,
        "childName": "Salaries",
        "reference": "Corp",
        "gstApplicable": false,
        "transactions": []
    }],
    "__v": 0
}

How could I achieve this in MongoDB.

Thank you.

What I have tried:

I've tried this,

await Ledger
        .updateOne({ child: { $elemMatch: { _id: mongoose.Types.ObjectId(req.body._id) } } }, {
            $push: {
                "child.$[inner].transactions": {
                    transactionID: "shreyas",
                    date: "",
                    particulars: "To ",
                    voucherType: "Payments",
                    voucherNumber: "",
                    debit: 30,
                    credit: "" //Amount
                }
            }
        })
        .then(async(result) => {
            res.status(200).json({
                data: result
            })
        });
});