My friend is trying to buy ether on coinbase with a 200 dollar visa gift card and is having problems with it saying invalid card. Can you even buy ether on that website with a gift card?
I don't see why not, but as said above the card must be activated first. Also, coinbase charges a transaction fee, so you'd need to make sure the eth+fee is less than or equal to $200. Your friend won't be able to purchase a full $200 worth of eth.