Merchant will be charge 6% GST base on MDR offer by bank. example bank offer merchant 2.5% MDR (Merchant Discount Rate)

Let say u buy an item cost $100, when u pay using credit card & total will be $100 + $6(6%GST).

Merchant will be charge 6% base on $100 X 2.5%= $2.50 X 6%(GST) = $0.15 (merchant will need to absorb this)

Bank will remit payment to merchant $ 97.50 - $0.15 = final amount receive by merchant $ 97.35, another $0.15 bank will remit to Kastam.

That what i been brief by bank.