Enter an allocation structure

What causes this issue?

You require a settlement structure for settlement according to the
distribution rules you entered.

System Response

The system cannot save the settlement rule without a settlement
structure.

How to fix this error?

To enter a settlement structure, choose "Parameters" in the settlement
rule.
You can also store a default value in customizing, in the settlement
profile. When you create a settlement rule, the system copies this
default value.

Error message extract from SAP system. Copyright SAP SE.