Originally Posted by
SeeBuyFly
https://www.amazon.in/hfc/mobileRecharge
Usually accepts my amazon.com account Visa/MC with 2FA verification via PayU (also known as PayUp). However, it does not always work. AmEx always works.
Generally easier to pay for a year at a time.
On the recent trip to Bangalore I was able to recharge my Airtel SIM at a brick-and-mortar Airtel store with cash. But I had no luck at all using any electronic payment method (including Amazon, cited above).