A feature available on 3dcart was the ability to temporarily close the store (or only the checkout portion) from incoming traffic. This was intended to allow merchants to halt orders while the site was being designed and/or worked on. To get to this section of the admin, users would go to Settings ->Design ->Close Store
The feature is still available, but the naming of it was updated to be a bit more clear on its intention. It is now found by going to Settings ->Design ->Store Status.