Open deliveries exist for reservation &

What causes this issue?

The system has established that one or more deliveries already exist for
the reservation (for example, delivery &V2&).

System Response

Therefore, it is not possible to use the "delete reservation" function
or set the delete flag for the item.

How to fix this error?

First complete the deliveries, and then delete the reservation or set
the delete flag.

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.