Payment term & not permitted where tax base = net amount

What causes this issue?

Cash discount can be taken on installment items created according to
term of payment &V1&. This means that the net invoice value, which in
this case forms the tax base, is changed.
The calculated tax base amount is therefore wrong, and the document
cannot be posted.

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

System Response

Error message which prevents the document from being posted.

How to fix this error?

You can either enter a separate item for every installment or enter the
whole cash discount amount. However, the latter procedure is only
useful in situations where the same discount percentage rate applies to
all installments.

Error message extract from SAP system. Copyright SAP SE.