Valuation Category in extending a new material

Hello Experts,

We recently created a new plant and is extending a material to it. However, we are being required to enter a Valuation Category in Accounting 1 tab of MM01. In our reference plants, Valuation Category is set to blank and greyed out which is the correct set up.

Can you advise what table should be configured to make Val Cat not mandatory or a greyed field?