Hi,
I had same problem.
I managed to fix it by changing "Checking rule" by SPRO.
Go to SPRO.
Materials Management / Purchasing / Purchase Requisition / define screen layout at document level
now, you can play different "Required (mandatory) entry"
The question is, do you need to make a control on your net price when you create a PR.
I didn't.
Hope it helps. Regards,
Martin