I'm trying out something called Gua Sha.

I've always been curious about this, but I'm not usually the type to be particularly ambitious about things like this. However, since there's a challenge going on, I hurriedly grabbed a cheap one from Coupang. But how much pressure should I apply? I feel like it won't work if I go too gentle, but I'm scared I'll get bruised if I do it too hard. It's kind of ironic, isn't it?