What does "Require authentication for all Share Links" mean?

"Require authentication for all Share Links" means that when a URL is shared via the Share link at the top right corner, the person who receives the URL will be forced to sign in to InVision and must be on your list of members in the People tab in order to view the prototype.

In other words, if they want to view the share link URL, you will need to add them to your Member list.

If an Enterprise user clicks a share link for a prototype they're not authorized to view, they can request access.