You have to use your debit card and load balance to Amazon Pay.
- It will be stored under the money component of your wallet.
- Go to Credit card bill in Amazon Pay, select your card and choose payment mode as UPI.
- Select Other UPI IDs/Net banking.
- Enter your phone number@amazonpay as the UPI handle.
- Follow rest of the process to completion.
If you have Millennia DC you get 1% CB by default because you are loading your wallet and it is covered in card T&Cs.