How do I add free text to an invoice

I can show you how to do that, gdurhamandsons-y.

You can add the text in the Memo or Message on invoice field. Here's how:

1. Click the + New button, then choose Invoice.
2. From the Customer drop-down menu, select a customer. 
3. Review the invoice date and terms.
4. Enter the product/service, quantity, and rate.
5. Select a Tax option, then enter the text in the Memo or Message on invoice field.
6. When you're done, click Save and send or Save and close.

For more tips in customizing your invoices in QuickBooks Online, you can read this article: Customize sales forms.

Should you have any other concerns about your forms, please let me know and I'll help you out.