> I tell about UPI to my friends in Western countries, When they tell how easy and seamless Apple Pay has made their payments, they're often surprised that such system exists here […]

Western countries in your statement is probably mainly USA, as most of Europe has been using contactless payment via NFC for many years.

Apple Pay is effectively just using the phone’s NFC chip instead of that embedded in the debit/credit card, although it does bring one advantage: Because the iPhone has its own authentication system, you’re never asked for PIN code when paying with your phone, whereas paying with a debit/credit card will ask for PIN if the amount is above a certain threshold, or if it hasn’t asked for a long time.

I have been using payment apps in Asia, not India, but Apple Pay is definitely more seamless (or NFC enabled cards), as these only require you to hold them near the terminal, whereas a payment app require first being launched, and then either scanning a QR code and confirming, or bringing up your QR code to have the cashier scan it.

Don’t get me wrong: I am very much a fan of the concept of UPI, I am commenting just to clarify that universal payment interface with third party apps is different than NFC enabled payments, where I think it is really the latter, that your friends in Western countries are describing as seamless.