用php从网站目录下载

Question

I have an issue with downloading files with PHP. I think the download.php is not working and I need assistance. when I click download button, instead of downloading the file, it is trying to open it like a page and says it is not available in the server, yet it is there. this is the error message

website button

<a  href="download.php?id=<?=$results['file'];?>" ><button 
class="btn1">download</button></a>

download.php

if (isset($_POST['id'])) {
    $stat=$conn->prepare("SELECT * FROM complete WHERE id=?");
    $stat->bindParam(1,$id);
    $stat->execute();
    $data = $stat->fetch(PDO::FETCH_ASSOC);

    $file = 'files/'.$data['filename'];

    if (file_exists($file)) {
        header('Content-Description:'.$data['description']);
        header('Content-Type:'.$data['type']);
        header('Content-Disposition:'.$data['disposition'].';filename="'.basename($file).'"');
        header('Expires:'.$data['expires']);
        header('Cache-Control:'.$data['cache']);
        header('Pragma:'.$data['pragma']);
        header('Content-Length:'.filesize($file));
        readfile($file);
        exit();
    }
}
?>