Welcome to the QuickBooks Community, @cdaniels16.
I'll share some information on how purchase order (PO) works in QuickBooks Online (QBO).
By default, the PO will be tagged as closed once it's copied to a bill, even if it's a partial amount. To link the remaining amount to a bill, you'll want to manually change the status of the PO to Open. Here's how:
- Sign in to your QBO account.
- Click Expenses from the left menu, then select Expenses.
- Find and open the closed PO.
- From the status drop-down, select Open. Then, update the amount and the quantity and click Save.

- Once done, click Copy to Bill to link the remaining amount.
In addition, you'll want to ensure that the quantity and amount of the initial bill didn't exceed the quantity and amount of the purchase order.
You may want to run and customize the Transaction List by Date report in QBO. This will display all the money you've paid to a vendor for a particular date range.
Feel free to leave a comment below if you have other concerns or follow-up questions about converting PO to a bill. I'll be around to provide further assistance.