So I went to purchase keys and it keeps saying I have to pay with something opskins gifts card

So I bought a gift card and I am trying to figure out how to use it

If someone can help me and I buy the keys. After I sell the keys I'll give them a good donation

https://opskins.com/?loc=redeem_item_code

Buy keys here: https://opskins.com/?app=1912_1&loc=shop_search&search_item=key&sort=lh

Save your FG/donation. GL

Wow thanks so much!!! Just uploaded my gift card and it went to my account!