Sampler sound is not output while I'm using Serato DJ Pro. Why not?

The output for the sampler sound may not be set correctly.
Set the [DECK4/SAMPLER] selector switch to [SAMPLER].
Ensure that the output destination is selected for [OUTPUT] in the upper right of the sampler panel.

For details, refer to the Serato DJ Pro software manual.
You can read the Serato DJ Pro software manual [here].