After changing the mobile im unable to add and activate my bank account in google pay. Upi requires latest version like iPhone xs and above. How to rectify this issue in iPhone X

You'll HAVE to buy a newer, more modern iPhone if you have applications which require iOS 17. There is NO workaround. This is NOT an Apple issue. This is one mandated by your banking institution.

You can't. In general, banking applications require recent security protocols and aren't available for units on older OSes.

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UPI has decided to abandon support for older and recent iOS versions. In doing so, they have decided for you that you need a new iPhone.