Yes, the cashier can use your phone number associated with your Rewards account to look you up or, make sure to ask for a receipt at the time of your purchase. Your receipt will contain a barcode that can either be scanned into the app or the code can be entered manually into the app or on The Simple Greek Rewards website.  All receipts must be submitted within 72 hours and scans are limited to 2 scans every 2 hours.