Change the type of your input parameter back to "date" and convert the "BUDAT" value using the "date" function to a date.
E.g.
daysbetween('$$KEY_DATE$$', date("BUDAT"))
Change the type of your input parameter back to "date" and convert the "BUDAT" value using the "date" function to a date.
E.g.
daysbetween('$$KEY_DATE$$', date("BUDAT"))