I am not able to add my debit card on my apple pay

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

See -> 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)

Then 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)

Tells us more. What happens when you try? Are you seeing some error?