Want to create a Measure, Value want to insert in Rows under category

DeepakSharma_01 , First create a measure 

Off_Invoice =
CALCULATE(
SUM('Sales'[Gross Amount]) - SUM('Sales'[Net Amount]),
'Sales'[REV_REDUCTION_TYPE] = BLANK()
)

Than create a measure to display the Net Amount including Off_Invoice:

Net Amount with Off_Invoice =
IF(
ISBLANK('Sales'[REV_REDUCTION_TYPE]),
SUM('Sales'[Net Amount]) + [Off_Invoice],
SUM('Sales'[Net Amount])
)

Create a measure to display the REV_REDUCTION_TYPE including Off_Invoice:

REV_REDUCTION_TYPE with Off_Invoice =
IF(
ISBLANK('Sales'[REV_REDUCTION_TYPE]),
"Off_invoice",
'Sales'[REV_REDUCTION_TYPE]
)

Add Region to the Rows.
Add REV_REDUCTION_TYPE with Off_Invoice to the Rows.
Add Gross Amount to the Values.
Add Net Amount with Off_Invoice to the Values.