Some give credit for gift CARDS purchased, others for gift card money redeemed.

有些为礼品卡购物提供优惠，而另一些则是针对礼品卡兑换的现金。

youdao

Now that my music's living on there (minus all the one-hit wonders I purchased using iTunes gift cards), I appreciate it more.

ENGADGET: IRL: Nexus One, Sansa Clip Zip, DeLorme PN-60 and the HP TouchPad

Credits can be purchased via credit card, Paypal, mobile phone or through the gift cards currently being sold in Target retail stores around the U.S. Over 200 games and applications on Facebook currently use Facebook Credits system, according to Liu, spanning over 75 developers.

FORBES: Facebook Credits Opens Up to More Developers, Adds More Ways to Pay