AWS S3 Heroku nodejs - node.js

Question

I am running a nodejs application hosted on heroku where I want to be able to upload selected photos to AWS S3. I followed all the steps heroku gave, but am finding this error: "MissingRequiredParameter: Missing required key 'Bucket' in params"
Here's my code:
index.js
app.get('/sign-s3', (req, res) => {
const s3 = new aws.S3();
const fileName = req.query['file-name'];
const fileType = req.query['file-type'];
console.log(fileName, fileType)
const s3Params = {
Bucket: S3_BUCKET,
Key: fileName,
Expires: 60,
ContentType: fileType,
ACL: 'public-read'
};
s3.getSignedUrl('putObject', s3Params, (err, data) => {
if (err) {
console.log(err);
return res.end();
}
const returnData = {
signedRequest: data,
url: `https://${S3_BUCKET}.s3.amazonaws.com/${fileName}`
};
res.write(JSON.stringify(returnData));
res.end();
});
});
app.post('/save-details', (req, res) => {
res.send(req.body.username)
console.log(req.body.username)
});
here's my front end scripts
testing.ejs
<input type="file" id="file-input">
<p id="status">Please select a file</p>
<img style="border:1px solid gray;width:300px;" id="preview" src="/images/default.png">
<h2>Your information</h2>
<form method="POST" action="/save-details">
<input type="hidden" id="avatar-url" name="avatar-url" value="/images/default.png">
<input type="text" name="username" placeholder="Username"><br>
<input type="text" name="full-name" placeholder="Full name"><br><br>
<hr>
<h2>Save changes</h2>
<input type="submit" value="Update profile">
</form>
<script>
/*
Function to carry out the actual PUT request to S3 using the signed request from the app.
*/
function uploadFile(file, signedRequest, url){
const xhr = new XMLHttpRequest();
xhr.open('PUT', signedRequest);
xhr.onreadystatechange = () => {
if(xhr.readyState === 4){
if(xhr.status === 200){
document.getElementById('preview').src = url;
document.getElementById('avatar-url').value = url;
}
else{
alert('Could not upload file.');
}
}
};
xhr.send(file);
}
/*
Function to get the temporary signed request from the app.
If request successful, continue to upload the file using this signed
request.
*/
function getSignedRequest(file){
const xhr = new XMLHttpRequest();
xhr.open('GET', `/sign-s3?file-name=${file.name}&file-type=${file.type}`);
xhr.onreadystatechange = () => {
if(xhr.readyState === 4){
if(xhr.status === 200){
const response = JSON.parse(xhr.responseText);
uploadFile(file, response.signedRequest, response.url);
}
else{
alert('Could not get signed URL.');
}
}
};
xhr.send();
}
/*
Function called when file input updated. If there is a file selected, then
start upload procedure by asking for a signed request from the app.
*/
function initUpload(){
const files = document.getElementById('file-input').files;
const file = files[0];
if(file == null){
return alert('No file selected.');
}
getSignedRequest(file);
}
/*
Bind listeners when the page loads.
*/
(() => {
document.getElementById('file-input').onchange = initUpload;
})();
</script>
hopefully this helps, and thanks in advance.