External procurement not defined for valuation type &

What causes this issue?

External orders are not permissible for the
<GL:valuation_type>valuation type</> that has been determined by the
system for the specified <GL:valuation_area>valuation area</> or
<GL:valuation_category>valuation category</> of this material.

How to fix this error?

INCLUDE EINGABE_PRUEFEN_NA LANGUAGE EN
If necessary, contact your system administrator. The latter can check
the valuation type using the Customizing facility.
IF &DEVICE& = 'SCREEN'
<DS:SIMG.SIMG_CFMENUOLMWOMWC>Set up split valuation</>
ENDIF

Error message extract from SAP system. Copyright SAP SE.