Enter only one true account assignment

What causes this issue?

You made assignments to several objects in CO (cost center, order,
project etc.). &V3& of these have been created as true objects.

System Response

You are allowed only one account assignment for each cost-relevant
account.

How to fix this error?

Enter only one true account assignment.
INCLUDE 'CO_KONTIERUNGEN' OBJECT DOKU ID TX
The posting row affected is &V2& and the account is &V1&.

Error message extract from SAP system. Copyright SAP SE.