What is the root cause of 403 Forbibben error in Prod and how to solve it ?

Hello,

I am trying to upload images from my heroku symfony(php) app to my bucket.
Can you help us check the root cause for such issues?
We always run into such S3 bucket access issue. It will be highly appreciated if you can help check for us.

S3Exception: S3ResponseError: 403 Forbidden

<?xml version="1.0" encoding="UTF-8"?>

<Error><Code>AccessDenied</Code><Message>Access Denied</Message><RequestId>FJPC9Z4Y44ZEYMST</RequestId><HostId>om6ov6N7LoQNYm1zVn1bQ7g0eHVXhUf3UjmxxSVni3lPk94LSFDJ9tG4nKSFqsyRBGaxWF/FxYI=</HostId></Error>

Here the configurations of my application : https://stackoverflow.com/questions/69391992/why-heroku-symfony-app-fails-on-upload-to-s3