Yes, EduardA, I know how to add the Account Summary to a custom template.  That's not the problem. 

Please read my original request:

• Does anyone know how to get QuickBooks Online to use the default invoice template when importing invoices?

The issue occurs when importing invoices.  Quickbooks does not use the template marked as the default, it always used the "Modern" invoice; which has no way of adding an "Account Summary" section.

How do I get an "Account Summary" section included in an invoice that is created via the "import invoice" workflow?