The instructions for this function say 3 input parameters but the system wants something different.
What are the formats of your two date variables that you are passing as parameters?
Try using the DateValue formula instead of Date
Date is looking for the date as (year, month, day)
DateValue is looking for a date string ("2017-1-14")
=DATEDIF(DATEVALUE(DateA), DATEVALUE(DateB), "D")
Tried switching the date field to use YY-MM-DD and the method to DATEVALUE but it does not let me use DATEVALUE, requires DATE for some reason. I actually get a message that says "something is wrong" when i try to replace date is DATEVALUE.
How do I get a csv date from a date field?
DATEVALUE is looking for a 4 digit year
It worked for me when I assigned the date fields to be:
I applied a Field Rule to only show the calculation field when both date fields were selected because there was an error message on the form until both date fields were selected.
Don't know if that helps, but it's a work around!