Why I don’t add card in my wallet

See the following Apple articles:

Set up Apple Pay -> Set up Apple Pay - Apple Support

Countries and regions that support Apple Pay

Countries and regions that support Apple Pay - Apple Support (EG)

If you can't add a card to Apple Wallet to use with Apple Pay

If you can't add a card to Apple Wallet to use with Apple Pay - Apple Support

• Apple does not approve or decline cards for use with Apple Pay. If your card was declined, contact your bank or card issuer.

See -> About billing for Apple subscriptions and media products in India

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

See -> Payment methods you can use with your Apple ID

Payment methods you can use with your Apple ID – Apple Support (UK)

India

• Apple Account balance (from adding funds)
• Net Banking (adding funds only)
• UPI (adding funds only)

Then use / pay with your Apple Account balance, see: Add money to your Apple Account balance

Add money to your Apple Account balance - Apple Support

Please read my previous reply.

What happens when you try? Do you get an error? If so, what does it say?

If you get the Learn More popup that takes you to the support document you posted from when tapping on the (➕) icon, then make sure your iPhone is set to a country or region where Apple Pay is supported in Settings➜General➜Language & Region➜Region. click here ➜ Countries and regions that support Apple Pay - Apple Support

What happens when you try? Do you get an error? If so, what does it say?

If you get the Learn More popup that takes you to the support document you posted from when tapping on the (➕) icon, then make sure your iPhone is set to a country or region where Apple Pay is supported in Settings➜General➜Language & Region➜Region. click here ➜ Countries and regions that support Apple Pay - Apple Support

See what already posted.