There are 2 types of amazon cards available.
1. Amazon shopping voucher (used only for shopping)
2. Amazon gift card (used for bill payments and other merchant payments)
To buy using payzapp
1. Select voucher, denomination and add to cart
2. Checkout and pay either through card or payzapp wallet
3. If paying through payzapp wallet then you'll see option to either pay through wallet or saved cards on payzapp.
4. Post payment you'll get voucher code, just copy it and add it to amazon on amazon app or website