Data model &1, entity type &2: Invalid check table

What causes this issue?

For entity types with storage and use type <LS>3</> for which the check
table is predefined by the data element or domain, the other key fields
in the check table must be mapped using relationships with the
relationship type <LS>Leading</>. The assignment between the leading
entity type and the additional key field can only be made if the data
element being used or the related domain can be assigned uniquely. There
is no unique assignment in this case, since data element &V3& or the
related domain cannot be clearly identified in the check table &V4&.

System Response

The data model cannot be saved or activated.

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.