Logical system & must not be deleted

What causes this issue?

The logical system &v1& is still used in distribution model &v2&
(client &v3&).

System Response

The deletion cannot be carried out.

How to fix this error?

Confirm that the logical system &v1& is really no longer used. Delete
it first from distribution model &v2& (client &v3&), then delete it
here.

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.