如何在s3中写入存储桶中子文件夹的路径

I have a bucket called music in AWS S3 and I have a sub-folder within it called 15. I can reach this folder on the GUI however using the PHP SDK if I put the folder path of the sub folder 15 as music/15 I get an error. How do I write the path to a sub-folder within the bucket music?

The code below should help:

private function get_flist() {
    try {
        $result = $this->s3->getIterator('ListObjects', [
            'Bucket'    => $this->bucketmp3,
            'EncodingType'  => 'url'
        ]);
        return $result;
    } catch (Aws\Exception\S3Exception $e) {
        echo "There was an error getting list of files.
";
        print_r($e);
        return null; // error
    }
}

Note: bucketmp3=music/15