You'll need to set your template with the account summary as a default. Let me show you how.
Before anything else, let's review your templates and make sure that the Include on invoice box is checked. Here's how:
Once done, you can now set it as a default template. You can follow the steps below:
That's it! You're now able to set a default template for your invoices with the account summary.
You can also read this article for more information: How to Customise Invoices, Estimates, and Sales Receipts?
Always know that you can tag me in your comment if you have any other concerns.