It says grapeseed oil, must I use that kind of oil? Or is normal olive oil fine?

Depends greatly on whether you're heating it. If so, use only olive oil, coconut or avocado (in order). Absolutely NO seed oils!!

Avocado oil is neutral... that one might be worth a shot.

Olive oil will work but it has a stronger flavor than grapeseed oil, which is neutral-flavored, so it will alter the flavor a little bit (but not necessarily for the worse; it just depends on your preference).