More than one distribution rule; maintain using settlement rule only

What causes this issue?

For the current order, the settlement rule should be created, deleted,
or changed through the settlement fields in the master record
(settlement light). However, more than one distribution rule exists.

System Response

With "Settlement light" only one distribution rule exists. The system
therefore assumes, that the existing distribution rules were created
through the maintenance interface for the settlement rule.

How to fix this error?

Use the function "Settlement rule".
This could be a system error. Contact your system administrator.

Error message extract from SAP system. Copyright SAP SE.