If you create a Purchase Order by mistake, provided you haven't marked the order as placed, you can delete it.
1) Open the Purchase Order in question from the Purchase Orders page, by double-clicking on it, or single-clicking on the blue PO Number on the left.
2) Click on Actions, then on Delete Purchase Order.
3) It'll ask you to confirm that you definitely want to delete it – click Yes:
N.B. If you see a message like this, that means that the Purchase Order has already been marked as placed, meaning it can't be deleted:
