Calculate SLA Duration excluding weekend and holidays

Hello everyone , 

I'm trying to calculate the duration for each SLA KPI instance in Dynamics 365 , 

 so we have the created on date and succeeded on date , and i can calculate the duration without excluding weekends and holidays

I already tried this solution , but i think it's calculating (Saturday and Sunday ) as weekends and it's giving 0 as a result most of times : 

https://community.dynamics.com/enterprise/b/razdynamics365/archive/2017/01/30/calculate-duration-of-business-days-in-dynamics-365-crm

Any ideas  ?

THANKS .