noun
BAD : The other day I was given a gift certificate, but it was only worth two thousand yen.
GOOD : The other day I was given a gift voucher, but it was only worth two thousand yen.
◆◆◆
certificate = an official document that states certain facts about someone: 'a birth/marriage/death certificate', 'a certificate of health'
voucher = a kind of ticket that can be used instead of money: 'a gift/luncheon/travel voucher'.