There are already several (razorpay, paytm, payu) that do exactly that. They do charge 2% flat fee which is still high by Indian standards (comparing to cash an

There are already several (razorpay, paytm, payu) that do exactly that. They do charge 2% flat fee which is still high by Indian standards (comparing to cash and upi). So merchants do try custom solutions with bank gateways to reduce the fee.