Thanks for getting back to us, @abricoetzer.

It's possible that the item you've selected in the purchase order (PO) doesn't have an expense account. If that the case, ensure to choose one. This can be done by editing its details.

Here's how:

1. In QuickBooks Online (QBO), go to the Sales menu at the left pane to get to the Products and Services page.
2. Locate the item and tick Edit under the Action column.
3. At the bottom, place a checkmark in the Purchasing information, then choose an Expense account in the drop-down.
4. Hit Save and close to complete the process.

Once done, create a test PO again to double-check. Just in case, I'll add these articles for future reference:

• Change the account for a product/service item.
• Edit a product or service.

Reach out to me in the comment section below if you have any other issues or concerns, and I'll get back to you right away. I'm always here to assist. Have a great rest of the day!