Official comment
Note the difference between those posts; in my response to you where you asked about the license, I said the DJM is not supported as a mixer for performance mode. In the response to the recording, I said you could use it for free in export mode; the mixer is supported as an audio device there ... any audio device with an input is.
You connect the DJM via USB, assign the input as the recording source in rekordbox, click the button and away you go.