@Will Coburn There is an accounting preference for 'Bill in Advance of Receipt' that you will need to enable then you can generate a bill right after entering a PO. For how you want to manage holding payment prior to actually receiving the item would need some thought. It could be as simple as a checkbox on the bill for 'Item Received' and you are unable to approve a bill until this is checked or it can be much more nuances, but the approval workflow can certainly be customized to handle this scenario