Logical system & must not be deleted

What causes this issue?

The logical system &v1& is assigned to client &v2&.

System Response

The deletion cannot be carried out.

How to fix this error?

Confirm that system &v1& is really no longer used. Delete it first from
the client assignment &v2&, then delete it here.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.