Only beep sound when recording

Hello!

I hope you can help me with my problem. I am trying to record scratches in Audition with multitrack. I am usin Serato DJ and SL4 as interface. When I press record in the multitrack the only sound that is rcorded in one blank beep sound (as the one you get from the Serato control vinyl). It is probably some easy trick to fix the problem but I cant figure it out. I have MacBook Air 2017.

Thanks in advance!