How to make billing data mandatory

Hi all,

We person immoderate contented with retired interface owed to our invoices being saved without billing date. By default, it is being acceptable to GI day but it was discovered erstwhile a idiosyncratic deleted the date, that it tin inactive beryllium saved. No diary introduction are created but our API is inactive picking up the invoice.

How tin we marque the billing day changeable but mandatory successful the invoice?