Document item &1 &2 cannot be deleted (see long text)

What causes this issue?

You want to delete document item &V1&. This is not possible for one of
the following reasons:
The item has already been reduced (in whole or in part)
The item is not flagged as complete
The budget has already been increased
The document is in workflow
Items which have only just been created can be deleted without first
being flagged as complete,

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.