I have something to buy, how to I give csc in the trade? It's not showing up any option to give csc. :(

You need to turn the csc into gift cards then offer those onto the trade. Go to CS>items> cards are like the 3rd section down I want to say

Thanks for your help, I thought I would have to go and buy the card, I'm glad I could just turn my csc into the card :)