One object should be real for double-account assignments

What causes this issue?

You have entered two sender objects or receiver objects, both of which
are statistical. In this type of double account assignment one object
must be statistical and the other must be value-based.

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?

Check your entries and, if necessary, delete one of the two objects.

Error message extract from SAP system. Copyright SAP SE.