Include discount lines with AR invoice using FBDI Autoinvoice import

We would like to import discount lines from legacy system along with respective invoices(i.e. one +ve invoice line followed by -ve discount line for the same invoice number).we will not be calculating any discounts in Oracle. How to achieve using Autoinvoice FBDI import?

Challenges: If i try to pass invoice line amt with +ve and -ve amt in the same Autoinvoice sheet its failing with 'Duplicate invoice number' error.
I created Transaction Type: Invoice(sign:Any sign)and try to pass -ve amt for hte same invoice number.

Questions: How to capture discounts for AR invoice using Autoinvoice FBDI template without any discounts calculation in Oracle.