You have not yet assigned configuration values

What causes this issue?

You have identified the material as a configurable material in the
master record. The material is assigned to a material type other than
<LS>configurable material</>. Quantity-based inventory management is
defined for the material type assigned. Consequently, you can also
define this material as a variant by entering its material number as
the configurable material and assigning configuration values. However,
you must first have created the configuration parameters for the
material.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Set the <LS>Material is configurable</> indicator and save the material
master record.
On the <LS>Material Master</> screen, choose <LS>Environment</> ->
<LS>Configuration profile</> -> <LS>Create</>, and assign the variant
class to the material.
Call up the material master record again and enter the current material
number as the configurable material. The system automatically requests
you to assign configuration values.

Error message extract from SAP system. Copyright SAP SE.