Published and For sale describe two different parts of an artwork record.
Published is the publication state
A Published artwork has passed the publishing requirements and can be available to the public when its visibility settings allow it. A Draft remains private.
For sale is the availability state
For sale means the artwork is currently available to a collector. Other availability choices include Being held, Sold, Not for sale, and Not set.
A work can therefore be Published without being For sale. Publication controls whether the artwork can be public; availability describes whether it can currently be bought.
For website checkout
Direct checkout requires both conditions together: the artwork must be Published and available for sale, along with the other checkout requirements such as a valid price, supported purchase method, ready payment connection, tax setup, and buyer-facing shipping amount.