MongoDB TTL index never deletes records

I created an index as shown below and added a createdAt field to each new record added to the db. The records should be auto-deleted after 24 hours however I have waited days and nothing has been deleted.

db_connect.collection("records").createIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )

Adding record to the database

// Add info to db to search
    console.log("Adding info to database..");
    const otherAddress = e.target.address.value;
    const newRecord = {
        holderAddress: this.props.account,
        otherAddress: otherAddress,
        date: new Date(),
        data: encryptedData
    }
    await fetch("http://localhost:420/record/add", {
        method: "POST",
        headers: {
            "Content-Type": "application/json",
        },
        body: JSON.stringify(newRecord),
    }).catch(error => {
        window.alert(error);
    });

Endpoint it calls:

recordRoutes.route("/record/add").post(function (req, response) {
let db_connect = dbo.getDb();
let myobj = {
    holderAddress: req.body.holderAddress,
    otherAddress: req.body.otherAddress,
    data: req.body.data,
    createdAt: req.body.date
};
db_connect.collection("records").insertOne(myobj, function (err, res) {
    if (err) throw err;
    response.json(res);
});

Below is a screenshot from MongoDB website confirming there is an index..

Any help is greatly appreciated!