Is there a way to add to a customer invoice, a note field that can be used to enter information that only I will see - the customer will never see this?

Hi there, @tamarackriverarc.

Let me step in and help you add a field in your invoice. It depends on your form style if you want to show that field to your customer or not. You can remove the field on your form style as a workaround so that your customer can't see the note field. Here's how:

1. Go to the +New button, and select Invoice under the Customers column.
2. Click the Gear icon from the upper right corner.
3. Choose the + Add another field, then name the field by filling up in the box.
4. Click the blue highlighted Change what your customers see.
5. Select the Content menu, then click the pencil icon on the upper tile of the template.
6. Go to the + Custom field.
7. Remove the checkmark on the field you created recently.
8. Click the Done button.

For more detailed information about customizing your invoice template, you can refer to this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I also added an article that helps you import invoice custom form style in your QuickBooks Online account: Import custom form styles for invoices or estimates.

If you have additional questions, feel free to leave a message in the comment section. I'll be around here to help. Take care and have a great day!