Negative delivery costs not allowed

What causes this issue?

The <GL:delivery_costs>delivery costs</> for this item are negative.

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?

First check the <GL:conditions>conditions</> for the item.
It may be necessary to check the <GL:master_conditions>master
conditions</>(e.g. info record/contract) to which the item refers. For
example, it is possible that the delivery costs have been entered as an
absolute deduction (e.g. -10 USD).

Error message extract from SAP system. Copyright SAP SE.