Using Greek yogurt as a starter may result in sticky or slimy curd. It ultimately depends on what you're using as a starter. I highly recommend asking someone else for a bit of dahi as a starter, whether it's a family friend, a local Indian restaurant, or purchasing a container of dahi from an Indian store to make your first ever batch. It's almost like sourdough starter - you either make your own which you nurture for years, or you borrow someone else's.