Folder Invitation links (see screenshot below) will stop being supported in early May 2017. On this date, the folder invitation link will disappear from the folder settings page and existing folder invitation links will stop working.
Users will be able to achieve similar functionality with shared links. Shared links can be used as invitation links by enabling the setting "Allow anyone who can access this folder from a shared link to join as a collaborator" on the folder settings page (see screenshot below). If users in your enterprise have shared folder invitation links outside of Box, they should replace them with shared links with this setting enabled before early May 2017.