Executing gsutil command via nodejs not working - node.js

Question

I am trying to create an application in which json file containing details of request.body gets uploaded in the GCS Bucket.
Before this I simply created a txt file in the same directory as my code and tried to upload that txt file in the gcs bucket once I hit the API ... I was successful in that aspect.
I want to create a json file with content of req.body which i am able to create. Please find the below screen shot:
json gets created as soon as I hit the api via Postman
Problem is my gsutil command is not working .... Please help
Below is my app.js code
const path = require('path');
const app = express(),
bodyParser = require("body-parser"),
fs = require('fs'),
port = 8080;
const swaggerUi = require('swagger-ui-express');
const swaggerDocument = require('./swagger.json');
const customCss = fs.readFileSync((process.cwd()+"/swagger.css"), 'utf8');
const { exec } = require('child_process');
var date = new Date();
var month = date.getMonth() + 1;
month = (month < 10 ? '0' : '') + month;
var day = date.getDate();
day = (day < 10 ? '0' : '') + day;
var filename = 'ddr_requests_' + date.getFullYear() + '_' + month + '_' + day + '.json';
app.use(express.json());
app.use(bodyParser.json());
app.use('/api-docs', swaggerUi.serve, swaggerUi.setup(swaggerDocument, {customCss}));
app.get('/', (req,res) => {
res.send(`<h1>API Running on port ${port}</h1>`);
});
app.put('/api/ddr/:ticket_id', (req, res) => {
const ticket_id = req.params.ticket_id;
const requestBody = req.body;
if(!requestBody || !ticket_id){
res.status(404).send({message: 'There is an error'});
}
var fs = require('fs');
var writer = fs.createWriteStream(filename,{ 'flags': 'a'
, 'encoding': null
, 'mode': 0666
});
writer.write(JSON.stringify(requestBody)+',');
exec('gsutil -m cp -r ./'+filename+' gs://gibberish/'+ date.getFullYear() + '-' + month + '-' + day + '/', (err, stdout, stderr) => {
if (err) {
console.log('Error');
return;
}
// the *entire* stdout and stderr (buffered)
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
});
res.status(201).send('all ok');
});
app.listen(port, () => {
console.log(`Server listening on the port::::::${port}`);
});```