Project &1 contains released requests; project cannot be deleted

What causes this issue?

You cannot delete the CTS project &V1& because requests are assigned to
the project that have already been released.

System Response

Nothing is deleted.

How to fix this error?

Complete the project if you no longer need it.

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.