What could be the reason for not being able to change permissions with chmod in PHP after transferring files with FTP?

When transferring files via FTP, the ownership and permissions of the files may change, which can prevent you from being able to modify permissions using the `chmod` function in PHP. To solve this issue, you can try using the `ftp_chmod` function provided by the FTP extension in PHP to set the correct permissions after transferring the files.

// Connect to FTP server
$ftp = ftp_connect('ftp.example.com');
ftp_login($ftp, 'username', 'password');

// Transfer file
ftp_put($ftp, 'remote_file.txt', 'local_file.txt', FTP_BINARY);

// Set permissions after transfer
ftp_chmod($ftp, 0644, 'remote_file.txt');

// Close FTP connection
ftp_close($ftp);