DFF variable for Personalization not available- using Bind Variable

Summary:

In Expense report Header, we are trying to make a Seeded field(Authorization) as required based on the value in DFF field we added at the Expense Report Header. if the DFF value is Y, the Spend Authorization field should be required, else it will be optional.

Content (required):

Kindly advise how to find the DFF variable to be used in Expression Builder to make field required like how we use binding variables.

we created sandbox and edited the page for Personalization(expense report creation page).

on editing the Field structure in personalization, for the field Authorization, on the Required Option-> used Expression Builder tried below code but the codes are not working.