Trouble making In App purchase – Slime Evolution - raise your cute little slime! Review

Love this game but I cannot figure out how to watch the video to get gems, and I cannot purchase the rubies/gems although I have money on my account. Is there a way that I can buy the stuff in the store with USD? I can’t figure out how to purchase? I went in the forum but it’s all in Korean so I don’t know how to purchase anything? Thank you! Please help!
Review by Benevolent Dolphin on Slime Evolution - raise your cute little slime!.