Enter material for item category &

What causes this issue?

You want to create or change a component. You have not entered a
material for the component, even though the item category requires the
entry of a material (such as the item category 'stock component').

How to fix this error?

There are two options:
Enter a material for the component.
Change the item category of the component.

Error message extract from SAP system. Copyright SAP SE.