To get your Leap Motion working with Isadora, the simplest route is to install the Leap Motion Orion Beta v3.1.2 SDK. You will need to create an account with Leap Motion to download this file.

Installing the 2.3.1 version found on this page is also possible, but requires performing the not-too-complicated "hot fix" as described in the leap motion forum.

Note: Isadora's' Leap Motion Watcher actor does not work with the Leap Motion v4.0.0 Drivers