How to use IS_BEFORE with a date field and a single custom date, not two date fields?

I am trying to create a field that tells me is a date field, called Purchase Date, is before a specific date, 04/09/2023 (did/mm/yyyy, same format as the date field). This is my formula so far, but it returns a “0” (ie false) on all records so many what date I enter between the “ “ in the formula. 

IS_BEFORE({Start Date}, "04/09/2023")

How do I fix this? Thanks!