Account & requires an assignment to a CO object

What causes this issue?

All given account assignment objects (order, project) are defined as
statistical.

System Response

Statistical orders or projects are ignored when FI and CO are
reconciled. You must enter a cost center, order, project, or cost
object to which the costs are posted for CO postings.

How to fix this error?

Enter a cost center, an order, a project, or a cost object that is not
statistical. The posting row affected is &V2& and the account is &V1&.

Error message extract from SAP system. Copyright SAP SE.