Good day, @pharris1,
I'm here to share some information with you about the message you're receiving when editing a purchase order.
This happens when you set up a closing date for your books to restrict changes on your transactions. You can click Yes to confirm the changes. Otherwise, you'll need to edit the closing date on your settings to get rid of the reminder.
Check out to this article about closing your books in QuickBooks Online: How to close the books.
That will get you going, @pharris1. Please don't hesitate to post again if you have any other concerns about your transactions in QuickBooks Online. I'm always around whenever you need help.