Account no longer has a debit balance in dunning level &: &

What causes this issue?

As a result of changes to the dunning items (dunning level, dunning
block), a credit balance has occurred in the account dunning level.
This situation comes about if, for example, all the invoices which have
the same dunning level as the account dunning level are blocked for
dunning and simultaneously there are credit memos in the account which
have the same dunning level as the account dunning level. This causes
the balance to be reversed.

System Response

Message to the effect that the balance in the account dunning level is
no longer a debit balance.

How to fix this error?

You can reverse the changes that have caused the balance to be changed
or you can block the credit memos from dunning also, or even reduce
their dunning level to a level where a debit balance occurs in a lower
Note that, by doing this, you also reduce the account dunning level.

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.