How to add my credit card to iPhone to use tap an pay service in India

You cannot add a Debit/Credit Card to Apple Pay if the county that you have chosen under the Apple ID does not support it. (e.g. India)

Adding Credit/Debit Cards to Apple Wallet depends on the country that you live in --> Countries and regions that support Apple Pay

The tap-to-pay option is not available for any "Pay" in India. either Google Pay, Amazon Pay, Paytm, or UPI Pay does not have tap-to-pay options.

Google Pay (Tap to Pay) options are made available on demand in Star Bucks (Not all), 5 Star Hotels, or Hotels that foreign tourist visit frequently (Not tourist spots) and nowhere else.