How to use fputcsv()

Question

I am working with fputcsv(). My below code is working.

$data = array(
            'aaa,bbb,ccc,dddd',
            '123,456,789',
            '"aaa","bbb"',
        );

$fp = fopen('php://output', 'wb');
    
foreach ($data as $line) {
    $val = explode(",", $line);
    fputcsv($fp, $val);
}

fclose($fp);

But below code is not working.

$data = array(
            'aaa,bbb,ccc,dddd',
            '123,456,789',
            '"aaa","bbb"',
        );

$fp = fopen('php://output', 'wb');
    
foreach ($data as $line) {
    fputcsv($fp, $line);  // Here is the issue
}

fclose($fp);

I am getting empty output.