How can I fix Paytm issue on iPhone X running iOS 16.7.1?

You can't.

Paytm uses the UPI protocol which will only run on iOS 17 or higher. Your iPhone X can't run anything higher than 16.7.10.

If you want to use Paytm, you will need an iPhone XR or higher.

Hello,

Hmm, what is the payment issue?

Anyway, start here:

If you need to change or update your Apple Account payment method - Apple Support

Good luck.

The people who make the rules for the UPI payment system have apparently decided that all UPI payments on iPhones must take place on iOS 17 or higher. This rule applies to all apps that handle UPI payments. (When NPCI and the banks say “Jump!”, any app vendor who wants to continue to participate in the UPI system has to ask “How high?”)

If you want to make or receive UPI payments on your phone, you will need to replace the iPhone X with one which satisfies the UPI system’s requirements.