Select at least one distribution level.

What causes this issue?

In top-down distribution, data is distributed from one level to the
objects which lie "below" it. You must indicate at least one level
which you want to distribute down to.

How to fix this error?

On the "Processing Rules" screen, select at least one characteristic as
the distribution level.
Use the following examples as a guide:
INCLUDE 'COPA_TOP_DOWN_1' OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.