Serato Play Issue / No Controller In Use

I am having trouble playing a song out loud and cueing the other in my headphones.

I am using a Y Cabel Audio Splitter which is in the headphone aux of my laptop.
Headphones and an external speaker are connected to the Y Cabel.

Example:
If I have the fader completely to left playing a song out loud via the external speaker, the next song (on the right deck) being cued also plays out loud.

I should hear the left out loud / and the right in my ear.

The "Use Split Headphone Cabel" setting is enabled and the headphone icon on the deck I desire to cue is enabled as well.

Can someone explain why it is not working... Do PC settings need to be adjusted? Do I need a certain tyoe of Y Cabel? Any help will be greatly appreciated.

Thanks.