Pre Cue problem with DDJ-SR+ MacBook Pro

I have the same problem than this gentleman/lady:

“I have DJ PRO and Serato loaded on my new macbook pro. I have a Pioneer DDJ-SR and when I use Serato I can pre-cue using my headphones into the mixer. When I use DJAY PRO the pre-cue does not work. Any thoughts?”

When I turn “headphones mix” far left to “cue” nothing comes out. Any ideas?