In UPI, one account can be selected at a time which will be shown as default, but you can easily switch between multiple bank accounts whenever needed by tapping on 'change bank account'.
If you don't transact as much in the particular number then they give enamorous CB offers once you daily for 2 or 3 weeks then it'll be converted in shopping discount coupon this is what happens in my case
Amazon not providing good offers to me they didn't offer me a cash back of 10 they always offer me get flat 50 cash back on your next shopping via Amazon pay upi...