Force download Zip file results corrupted - php

Question

I'm trying to force a zip-file's download after some checks ( hash , expiration date, download's number ) .
The link of the page contains the id ( hash ) to validate the download.
For example:
www.example.com/download.php?id=505fbeabfd97c0ab15a016d68512d8df5acdedd6e6cc6
Everything works, but the file is corrupted.
If I try to eliminate all checks and the connection to the database, the zip downloaded is ok.
Here's the code:
<?php
$maxdownloads = "80";
// Set the key's viable duration in seconds (86400 seconds = 24 hours)
$maxtime = "2592000";
require ('connect.php');
if(get_magic_quotes_gpc()) {
$id = stripslashes($_GET['id']);
}else{
$id = $_GET['id'];
}
echo $id;
// Get the key, timestamp, and number of downloads from the database
$query = sprintf("SELECT * FROM digital_orders WHERE hash= '%s'",
mysqli_real_escape_string($conn,$id));
$result = $conn->query($query);
$row = $result->fetch_assoc();
if (!$row) {
echo "The download key you are using is invalid.";
}else{
$timecheck = date('U') - $row['date'];
echo $timecheck;
if ($timecheck >= $maxtime) {
echo "This key has expired (exceeded time allotted).<br />";
}else{
$downloads = $row['download'];
echo $downloads;
$downloads += 1;
if ($downloads > $maxdownloads) {
echo "This key has expired (exceeded allowed downloads<br/>";
}else{
$sql = sprintf("UPDATE digital_orders SET download .$downloads."' WHERE hash= '%s'",
mysqli_real_escape_string($conn,$id));
$incrementdownloads = $conn->query($sql);
$result->close();
// chiusura della connessione
$conn->close();
// Debug echo "Key validated.";
// Force the browser to start the download automatically
/*
Variables:
$file = real name of actual download file on the server
$filename = new name of local download file - this is what the visitor's file will actually be called when he/she saves it
*/
// Get parameters
$file = "dante.zip"; // Decode URL-encoded string
$filename = "foto.zip";
$filepath = "digital_orders/Dante/" . $file;
// Process download
if(file_exists($filepath)) {
ob_start();
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="'.$filename.'"');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($filepath));
flush(); // Flush system output buffer
ob_end_clean();
readfile($filepath);
exit;
}
}
}
}
?>
If I try to open the zip file that works with note-pad there is :
PK
ûe‹L dante.txtPK
ûe‹L $ dante.txt
CdÔ‹‚ÑÓCdÔ‹‚ÑÓÆ‹‚ÑÓPK [
'
If I try to open the corrupted zip file there is:
505fbeabfd97c0ab15a016d68512d8df5acdedd6e6cc61226822PK
ûe‹L dante.txtPK
ûe‹L $ dante.txt
CdÔ‹‚ÑÓCdÔ‹‚ÑÓÆ‹‚ÑÓPK [
Any suggestion? '