Use the Amend deliveries option to cancel a purchase order.
You can only cancel the order is the status is On-Order. If the order is complete, delete or reverse the order, adjust your stock and raise the order again.
Cause
Resolution
Cancel an order
Go to Purchase orders,select the purchase order to cancel, then select Amend deliveries.
Select Off Order then Close.
This changes the status to CANCEL in the On-Order column.