In a course business, fulfilment is not a packing slip. It is the student getting into the LMS, and getting out of it if the payment does not stand. When fulfilment is a zap, it is optional in practice, because zaps can be off. When it is part of the order, the cart and the classroom tell the same story.
RobinCart calls this a fulfilment engine on purpose. It is the piece general carts leave to Zapier, and the piece course creators notice the first time a paying student cannot log in.