You can only cancel uncompleted purchase orders.

Open the purchase order and select the Cancel Order button.

When you cancel the order, the status of the purchase order will be changed to Completed with Cancellations. Any outstanding goods receipts quantities linked to the order will be set to zero.

Orders with partial receipts

All Goods Receipts linked to the order, that were not completed, will now be automatically completed with a quantity of zero received and zero on back order. Any previously completed receipts will remain untouched.