Manufacturer part number management not set for your firm's own material

What causes this issue?

For a manufacturer part to refer to one of your company's own materials,
a <DS:DE.MPROF>manufacturer part profile</> must be specified. However,
no such profile has been assigned to your 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?

Assign a manufacturer part profile to your company's material. In the
standard SAP system, the <LS>Manufacturer part profile</> field appears
on the <LS>Purchasing</> screen in the material master.

Error message extract from SAP system. Copyright SAP SE.