How do you properly use "batchUpdate" ?

I've been trying to find usable information for a few hours now but nothing. I want to use batchUpdate to update my cells. So far so good but it never really works the way I want it to. I can log in but nothing happens after (I should note that I'm working on AWS Lambda) :

`// import libraries and packagaes
const fs = require("fs");
const { google } = require("googleapis");
const pKey = require("./credentials.json");

exports.handler = (event) => {
updateCells(jwtClient);
};

// login with service account
let jwtClient = new google.auth.JWT(pKey.client_id, null, pKey.private_key, [
"https://www.googleapis.com/auth/spreadsheets",
]);
// authenticate request
jwtClient.authorize(function (err, tokens) {
if (err) {
console.log(err);
return;
} else {
console.log("Successfully connected!");
}
});

// batchUpdate (UpdateCellsRequest)
function updateCells(auth) {
// get payload
var payloadArray = fs.readFileSync("./test.csv").toString().split("\n");
const sheets = google.sheets({ version: "v4", auth: jwtClient });
sheets.spreadsheets.values.batchUpdate({
spreadsheetId: "ID",
resource: {
requests: [
{
updateCells: {
fields: "*",
rows: [
{
values: [
{
userEnteredValue: {
stringValue: "Some string",
},
},
],
},
],
range: {
sheetId: 0,
},
},
},
],
},
});
}
`
I used the request object from the documentation sites generator/ test box. Does anyone know how to make this work or point me to the right direction? Thank you in advance