That's unfortunate. Don't know the exact problem here. Paytm, Gpay, Bharatpe merchant QRs work fine but only Phonepe has this problem. Did you encounter any Phonepe merchant QR that works with credit UPI ?
Bigbasket is more often than not cheaper than Amazon fresh. BB also have regional foods and groceries. 1MG is a little expensive than say FK health plus but it has bank tie ups so CC instant discount offers.