Can I setup default payment instructions on my invoices to avoid entering them each time?

Yes, you can set up a default payment instruction on your invoices in QuickBooks Online (QBO), northernplanners. I'll gladly show you how to do this below.

You can specify a payment instruction on your invoices through the Message on invoice field. Let's customize the form's Content section to do this. By doing so, there's no need for you to enter the information you want to convey each time. 

Here's how to customize your invoice with the old layout:

1. Go to Settings ⚙ and then select Custom form styles.
2. Select the invoice template you'd like to edit or choose the New style option to create a new invoice template.
3. Go to the Content section.
4. Choose the footer on the sample form to start editing that section.
5. Enter the payment instruction in the Message to customer on box.
6. Whenever you're ready to save your changes, select Done. 

In case you have the new invoice layout, please see this article to guide you on how to add specific information to your sales form: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Additionally, once your customer pays your invoice, record that transaction to balance your income and sales accounts. For a complete guide on how to do this, you can check out this article: Record invoice payments in QuickBooks Online.

Please know that I'm always ready to back you up if you need more help customizing and managing invoices in QBO. I'll keep the thread open so you can comment back.