Retailers may offer special deals that allow you to save money by pre-purchasing a set number of items at a cheaper price. Those are displayed in the “Make a saving” section of your retailer space and are often referred to as in-app purchases.
They usually come in the form of a “buy X get Y free” offer, allowing you to save money on items you would buy anyway. The items you pre-purchase are then turned into vouchers, ready to be redeemed whenever you feel like it - you don’t have to use them straight away!
For example if you bulk buy 10 lunches for the price of 7, you will instantly be issued 10 separate lunch vouchers redeemable over a period of time. After scanning the voucher QR code, 1 voucher will automatically be deducted from the total, leaving you with 9 vouchers. Check out the screen of your favourite retailer and see if there is any good bargain on display!