Notification(s) already assigned to an order

What causes this issue?

You want to create an order for one or more notifications, that have
however, already been assigned to orders.

System Response

INCLUDE KEINE-FUNKTION OBJECT DOKU ID TX LANGUAGE EN

How to fix this error?

You can only select notifications that have not yet been assigned to an
order.

Error message extract from SAP system. Copyright SAP SE.