System cannot calculate cash discount base amount; enter it

What causes this issue?

You want to determine the cash discount base of the open item account
line items. This can, however, not be done automatically in certain
cases. For example, if the open item account line item for which the
amount qualifying for cash discount is to be determined is on the same
side of the account as all G/L account items liable to cash discount.

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?

Enter the cash discount base amount in the open item account line
items.

Error message extract from SAP system. Copyright SAP SE.