I received a few eBay gift cards for Christmas and wanted to use them to purchase some mining equipment. Apparently you cannot due to eBay terms and conditions regarding currency...
"This code can't be applied to some of your items."
I am guessing these terms are being triggered by mining equipment:
The Gift Card may not be used to pay eBay service fees. The Gift Card also may not be used to buy eBay Gift Cards, third party gift cards, gift certificates, coupons, coins, paper money, virtual currency, or items generally considered to be "bullion" (for example, gold, silver, and other precious metals in the form of coins, bars, or ingots).
https://pages.ebay.com/giftcard/terms_conditions.html