User can fully undo receiving if all the items received in the beginning is not used/committed in Sales or have enough stock in the WMS. Otherwise it will give you a message unable to undo fully and will be partial undo .
Go to Receiving register:
1. In the example below, user unable to fully undo PO because some if the item is already used (highlighted yellow). User need to trace back and release the order. If the order is already closed then user need to do stock adjustment to add back the stock so that the PO have enough qty to undo.
2.Example of lines which is still not fully undo highlighted in yellow (Rec column still not 0). Item GRHA need 312 in stock In the location MELB-PICK to enable undo this.
3. Trace back GRHA to check the stock , there is only 238 available . User need to release the committed to have enough qty or do stock adjustment to add back 312.
Normally if sale is picked/packed /RTP, you can release the item . IF the sale already found closed with 312 qty., the stock adjustment needed to put back the qty and undo the PO.