Segmentation not possible for material &1, &2; see long text

What causes this issue?

Material is relevant for
<DS:GLOS.52B4FFCC5E910882E10000000A421392>segmentation</> but one of
the following is true:
Plant is not specified at the item level

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

<DS:GLOS.52B8D39C99790881E10000000A421392>Segmentation strategy</> is
not maintained or fixed for the material in the material master

System Response

How to fix this error?

Based on the diagnosis, do one of the following:
If plant is not specified, specify the plant where the material is
maintained.
If segmentation strategy is not maintained or fixed for the material in
the material master, assign and fix the relevant segmentation strategy.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.