When a user is visiting a page that she does not have access to, the DAP error message (with the DAP "Lock" image) is shown, which says "Click here to get access". That text "Click here to get access" will link to this Global Sales Page URL.

NOTE: This is used only if DAP cannot figure out, at a product level, as to which sales page URL to choose when the page or post being accessed is part of multiple DAP products.

This is a global setting. You can also over-ride this at a Product level, by modifying the "Sales Page URL" on the Product page.