Thanks for the heads up on the code reselling risk. That was my biggest worry with generic coupon codes too.

To solve this, I decided against just using a 'coupon' on the main checkout. Instead, I set up a completely separate payment flow (Topmate) specifically for India that requires local UPI payment methods.

My theory is that the requirement to use a local Indian payment method acts as a 'natural geoblock' against arbitrage. Interesting to hear that India didn't convert well for you even with PPP—I'll keep my expectations in check.