Cannot hear from my headphone the incoming song

Hi Commnity,

I am new to Mixing and recently bought the DDJ-FLX4. I have connected to my speakers and have no issues hearing the music currently playing. The issue is that I cannot hear the incoming song in my headphone.

I'm attaching a picture on when of the configuration when a song is playing on deck 1 and I cannot hear the song playing in Deck 2 on my headphones.

thanks for any insights on this.