Try this:
$df = fopen($filepath, 'w');
fprintf($df, chr(0xEF).chr(0xBB).chr(0xBF));
fputcsv($df, array($coupon->code, $discount->label));
the line fprintf($df, chr(0xEF).chr(0xBB).chr(0xBF)); writes file header for correct encoding.
Try this:
$df = fopen($filepath, 'w');
fprintf($df, chr(0xEF).chr(0xBB).chr(0xBF));
fputcsv($df, array($coupon->code, $discount->label));
the line fprintf($df, chr(0xEF).chr(0xBB).chr(0xBF)); writes file header for correct encoding.