If you wanted to do IR directly for a purchase order without posting the GR, you can achive this functionality at SPRO level or master data level or even at purhase order level.
Controls in IMG activity:
Option1: Account assignment category level
Path-> IMG-> MM-> Purchasing-> Account assignment-> Maintain account assignment categories
Note: Since we cannot make any changes to the item category as per standard SAP, we can just verify whether the item category used in P.O allows IR without GR or not.
Path-> IMG-> MM-> Purchasing->Define external representation of item categories
Controls in master data level:
Option1: Vendor master: (purchasing data view)
Option2: Purchase info record (purchasing org data 1 view):
Purchase order control: If P.O is already created in the system and you wanted to IR directly without GR posting,
then uncheck the ‘GR-based IV’ check box in the P.O item invoice tab as shown below.