Purchase order for a Service Item

Hi,

We are on Oracle R12.1.3.

I wish to raise Purchase order for a service which I wish to avail. I have created an Item number for the service. It is a purchased/purchasable item but not Inventory item. However, when I select Service as Type in the Purchase order screen, the 'Item' field gets greyed out and I can not enter the part number.

I do not wish to make a Receipt for the item. I will manually book the Service invoice in AP.

I need item number for a specific purpose of tracking the service transactions.

I want to use core purchasing module