Movement type & can only be carried out for structured material

What causes this issue?

You have chosen a movement type (317, 318, 319, 320) with which you can
only split or join <DS:GLOS.structured_material>structured material</>.
The material you have entered is not a structured 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?

INCLUDE NA_EINGABE_PR_FEN

Error message extract from SAP system. Copyright SAP SE.