upload failed: x.txt to s3://mybucket/x.txt An error occurred (InvalidTokenId) when calling the PutObject operation: The security token included in the request is invalid

Of course, it can be many and many things. However in the case of local instance of minio it's probably just a few. You might want to check that `AWS_SESSION_TOKEN` is not set. If it's set either unset it or provide a valid token.