The only one I could get to work was my Amex. That triggered the SMS passcode to complete the booking process.

However, when I clicked through from Google Flights to purchase a Vustara ticket that worked fine with my Citi MC. I’d suggest using that as an alternative.

All bookings done directly with the airlines in question. In retrospect, I’d avoid Indigo like the plague in the future and stick to Vistara if I ever go back to India.