Error in adding file to a bucket

If this worked before and no longer, the most likely is that it is a permission error, check the IAM role or the access keys that are used to give permissions.

If you are in the development process, check the documentation to understand how it works and the permissions you need to achieve it. For instance: https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/s3-example-photo-album.html