Hello, I got an 800 dollars travel voucher from delta for being bumped in last April. I recently booked a flight for 650 dollars using the voucher, so I got 150 left on it. I was wondering if I can use that money for something besides another flight ticket. For example a hotel room or an upgrade? I'm pretty sure it's usable for booking flights only, but I just want to make sure I'm not missing something. Thanks in advance!