In the DOO AR invoice with discount line, Assessable Value should be passed as Unit price

In the AR invoice (Created through Import Invoice, Source: Distributed Order Orchestration), 2 lines are passed for discounted lines:

1. The 1st line shows Assessable value as List Price(Ex. 100)
2. The 2nd line show Assessable value as Discount price with - value(Ex -10)

Due to this tax is calculated on 100 -10 value and not on 90 which is causing rounding off issues between SO and AR invoice.

We tried to implement Service Mappings to manage Assessable value but we need a way to put if else condition in Service Mapping expression to implement the below solution:

For the 1st line net price should be passed in Assessable value (Ex 90)