I am not able to find Google Pay in App Store ?

but still I am not able to download as I do with other apps from my Apple store in my iphone

That would have to do with -> About billing for Apple subscriptions and media products in India

About billing for Apple subscriptions and media products in India - Apple Support

India

•           Apple ID balance (from adding funds)

•           Net Banking (adding funds only)

•           UPI (adding funds only)

You can use / pay with your Apple ID balance, see the following Apple articles: Add money to your Apple ID balance

Add money to your Apple ID balance - Apple Support (IN)

Did you set your phone up with an Apple ID based in India or the UK? If your Apple ID is in the UK, you will need to set up an additional Indian Apple ID just to install Indian banking applications, of which Google Pay is one, from the Indian Apple store. The two IDs can reside simultaneously in your one iPhone.

Check here ⤵️

See -> https://apps.apple.com/us/app/google-pay-save-pay-manage/id1193357041

See also -> https://www.thehindubusinessline.com/money-and-banking/google-pay-is-back-up-on-the-app-store-in-india/article62192787.ece

See -> Google Pay Is Again Available For iPhone Users In India, but . . .

See -> https://pay.google.com/about/