&1 is to be delivered to the customer, &3 not

What causes this issue?

The packages of the referencing object and the object being referred to
are not compatible:
&V1& belongs to package &V2& that is to be delivered to customers.
&V3& belongs to package &V4& that is not relevant for customer delivery
(e.g. test package, local private objects, etc.)
This constellation means that the object referred to would not exist in
the customer's system.

System Response

An error message is issued.

How to fix this error?

Change the package of the object being referred to or chose a different
object.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.