I am not able to add my debit 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)

Set up Apple Pay in Wallet on iPhone

Set up Apple Pay in Wallet on iPhone – Apple Support (UK)

Apple Pay participating banks in Africa, Europe, and the Middle East

Apple Pay participating banks in Africa, Europe, and the Middle East - Apple Support

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

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: Add money to your Apple ID balance

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

Check if your country supports Apple Pay AND if your card issuer is among the partecipating banks:--> Countries and regions that support Apple Pay - Apple Support

Should be this case, set up your Apple Pay, using these instructions:--> Set up Apple Pay - Apple Support

Regards

Giulio