2.5% up to 400. So, make a payment of 16000 (16000*2.5% = 400) using your debit card to earn 400 cashback points.
Tip: First, make a small test payment of 100 rupees since the failure rate on unipay is quite high, and you wouldn't want your money to get stuck there for days. Once, that 100 rupees transaction gets settled (it will settle instantly), proceed with the rest amount.