AWS IAM policy that grants the necessary permissions for the s3 sync CLI command.

aws-s3-sync-iam-permissions.json

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Resource": [
                "arn:aws:s3:::YOUR_BUCKET_NAME",
                "arn:aws:s3:::YOUR_BUCKET_NAME/*"
            ],
            "Sid": "AllowSync",
            "Effect": "Allow",
            "Action": [
                "s3:DeleteObject",
                "s3:GetBucketLocation",
                "s3:GetObject",
                "s3:ListBucket",
                "s3:PutObject"
            ]
        }
    ]
}