A Purchase Order must be 'Received' before it can be paid.
Once the Purchase Order has been approved and the items/expenses have been all or partially received, find the Purchase Order in NetSuite and click the 'Receive' button at the top:
At the bottom of the next form, check off ('Receive') any Items or Expenses that were received:
Once complete, Save the form. If the Purchase Order is received, the status will change to 'Pending Billing'.