Calculate Duration (days) between two dates but only calculate weekdays.

Can you explain why the WeekDaySub is not working for you?  Can you tell us an example values for the two dates fields and the result and the result that you expect?

Note that you may need to add 1 to the result to get the result you expect.  For example

e.g. 2-1 =1
similarly, e. g. Tuesday - Monday = 1 day.  But you may want to call that 2 days if you count both the Monday and the Tuesday as a Day.