As a result of your changes, dunning notice is no longer printed

What causes this issue?

You have made changes to the dunning notice which mean that it can no
longer be printed. It is not printed for one of the following reasons:
All items have dunning level 0.
The minimum amount for a dunning notice is no longer reached, or a
debit balance is not given.

How to fix this error?

In the dunning level field, enter the new dunning level of the item if
the field is empty.
If you want to know why the dunning notice is not printed, choose the
function "Check dunning notice".
If you do not want the dunning notice to be printed, assign a dunning
block in the dunning header.

Error message extract from SAP system. Copyright SAP SE.