-- Adds 'due_soon' as a valid status alongside the existing six. MySQL
-- requires the full enum value list to modify one, but this is purely
-- additive — no existing row's value changes, and nothing is removed.
ALTER TABLE monthly_invoices
    MODIFY COLUMN status ENUM('upcoming', 'pending', 'due_soon', 'partially_paid', 'paid', 'overdue', 'cancelled')
        NOT NULL DEFAULT 'upcoming';