If it’s one of the 3 reminder messages for overdue invoices you can modify the base template to show the balance.
If you go to the “Account Settings” menu and select the option “Routine Emails”, you will see a list of email templates. The 1st, 2nd and 3rd Overdue Invoice Reminders are listed separately.
This is the default text.
Dear @FirstName@,
This is just to remind you that the following invoice is now overdue.
@DirectInvoiceLink@
Additional Invoice Details
Invoice: @InvoiceNumber@
Due Date: @InvoiceDueDate@
Total Amount: @InvoiceTotalAmount@
You also have the token @InvoiceTotalBalance@, so you could edit this template and add the line:
Balance Remaining: @InvoiceTotalBalance@.