NETWORKDAYS Logic In BI Report

Hi ,
As a Business requirement we want to get the Working days between 2 days.
I tried to get this using below query. But getting 0 as output.

(select count(*)
from table(per_availability_details.get_schedule_details
(
p_resource_type => 'ASSIGN'
,p_resource_id => paam.assignment_id
,p_period_start =>PPOS.CREATION_DATE
,p_period_end =>PPOS.date_start ) ) ) working_days

Request to help to get for same.

Thank you.