Hi, @cirrusmarketing. 

You're on the right track in setting a customized template as default to show the SKU of a product or service. I'm here to further assist you on this.

When you create a customized template for your printed invoice, you can choose which fields to include, such as the SKU field. If you have set your default template to show the SKU for a product or service, don't worry, as it will still appear on the printed form, even if it is not visible on the invoice sheet. Furthermore, if you use the old layout when creating invoices, there is an additional step to display the SKU field.

1. In your invoice sheet, go to the Gear icon.
2. Scroll down to Optional Columns.
3. Put a checkmark on the SKU under Product/Service.

Please refer to the image below:

To check if the SKU will be applied to your printed invoice, you can click on Print preview. Also, if you need assistance changing SKU for a product or service, you can do so when editing a product or service.

I have included an article on adding custom fields to your transaction sheets to help you track important information: Create and edit custom fields in QuickBooks Online Advanced.

Let me know if you need further assistance customizing your invoice through the reply button. I'd be glad to assist. Take care.