Fixed price co-product indicator cannot be set

What causes this issue?

Although you have indicated the material is a fixed-price co-product,
you have not defined the material itself as a
<DS:GLOS.co-product>co-product</>.
You can only set the <LS>Fixed-price co-product</> indicator if you set
the <DS:DE.KZKUPMAT>Co-product</> indicator for the material at the
same time.

System Response

The material is not saved with this setting.

How to fix this error?

Set the <LS>Co-product</> indicator, or remove the <LS>Fixed-price
co-product</> indicator.

Error message extract from SAP system. Copyright SAP SE.