Hi there, @dsourelis!

With QuickBooks Desktop, there isn't a warning message if the amounts of your purchase order don't match with your bill.

This is because you'll have to create first your purchase order before your bill. From there, you can automatically apply the content of your purchase order to your bill.

In addition, you can easily pull up all the bills for that same vendor by clicking Run QuickReport within your purchase order.

Lastly, here's a screenshot for your visual reference. Also, an article you can read to learn more about creating purchase orders: Create a Purchase Order.

Feel free to leave a comment below if you have any other questions about purchase orders. It'll be always my pleasure to lend a hand.