Hi,

Thanks for the additional information that the invoice is coming from PO to AP.

The discount base in PO does not include taxes. Therefore, the invoice it sends to AP uses the discount base before taxes also and this information cannot be edited in AP unless the terms are changed (blanked out).

Probably the best way to work around this is to blank out the Terms on the Totals tab in PO when the invoice is being created. This will make the discount Base field available for edit. You can increase the discount base to the total amount of the invoice including tax at this time. Then, it will be sent to AP that way.