Help related Purchase Order

Hello Friends,

Please can you help me about below points-

  1. When we go to the PO=>Posting Button=>PurchaseOrder.

how to display the PO items On PurcheditLine Form=>Line Tab (i.e which method is called).

  1. When we post the packing list which method is called.

3 How to change the status of PO i.e. Open/received/invoiced.

Thanks