You can set the invoices past due reminders for yourself from User Settings > Reminders that show up later in the Reminders screen. However, note that reminders don’t appear until the selected item is outstanding for a full 24 hours. Reminders are removed from the screen soon after they are read.
BQE CORE also supports automated emails sent to clients for past due invoices. You can customize when these reminders are sent, choosing to dispatch them before the invoice due date, exactly on the due date, or after the due date has passed. To start using automated invoice reminders, you will need to enable and manage them through CORE by navigating to Settings > Billing & Invoices > Accounts Receivable. You can enable this option up at the client level as well as the invoice level.