Error on changing item category from a material PR - network

Dear experts,

I am currently facing an issue when I try to change the material item category on a network using CN22 transaction.

When I add the material and click enter, system fill in the item category "L" automatically.

However, the materials management team from the company I work informed that the correct data should be "N".

When I change the item category from "L" to "N" system does not allow me to create the network activity via "PReq+Res - WBS elem.".

If the PR item is not created via "PReq+Res - WBS elem.", system does not generate the PO.

Is this an issue on material register on SAP?

Is it possible to check the item category assigned for the material on MM03 transaction?

What transaction can I use to check the item category assigned for the material?