The expression editor will show you how it is evaluating your expression at the bottom of the screen. It will say OK when it's good to go, or will show errors. Typically for things like dates you might need to wrap them with single quotes so they come out look like they need division done
If(monthYear > 12/5/2021
Of it might show 0 or something because the value is jacked up.
If you wrap '$(vFrom)' it will add the single quotes around the value so the bottom of the screen should show