Property '&1' of entity type '&2' uses aggregation function

What causes this issue?

Property "&V1&" uses aggregation function but the entity type "&V2&" has
no aggregation semantic.

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?

Add semantic "aggregation" to the entity type "&V2&".

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.