RE: How to close partially received purchase order in dynamics 365 business central.
Ng,
When a Purchase Order is partially Received and you would like to close out the remaining unreceived quantities follow these steps:
1. Locate the Purchase Order
2. If the remaining quantity for the Item Line (Purchase Line) will NOT be received and other Lines will be, ReOpen the Purchase Order and on the Item Line change the Quantity to match the Received Quantity. Release the Purchase Order.
3. If the ENTIRE remaining quantity for the Purchase Order will NOT be received, first YOU MUST have INVOICED the Received Quantity. Then click the Trash Can icon to delete the Purchase Order document.

Hope this helps.
Thanks,
Steve