There are three things to consider: settings, operation, and connection.

Please check each in the following order:

1) Confirm the settings on the Serato DJ Pro screen

1. Click the icon in [My Serato] in the upper right of the screen.
2. Check that [Serato DJ Pro is activated] and [DDJ-FLX6] are shown on the screen.

If not, read the DDJ-FLX6 FAQ >[Troubleshooting_Serato DJ Pro] > "The Serato DJ Pro screen does not react when the DDJ-FLX6 is connected.".

2) Check the volume level operation

1. Play a track.
2. Set the TRIM knob to the center (12 o’clock).
3. Slide the channel fader to the top.
4. Slide the crossfader to the center.
5. Turn the MASTER LEVEL knob to 2 o'clock.

If you don’t hear any sound from the headphones at this point, check the following:

6. Turn the HEADPHONES MIX knob to the center.
7. Turn the HEADPHONES LEVEL knob all the way to the left.
8. Press the MASTER CUE button.
9. Turn the HEADPHONES LEVEL knob slowly to the right.

3) Check the connection of speakers and headphones

For details, refer to [Connections] in the Instruction Manual.

Even if you’ve already connected them, disconnect and reconnect them to make sure they’re properly connected.

*You can't output audio from PC/Mac speakers.

You can read the Instruction Manual [here].