System design interview - How online payment works using QR code?

QR code is common while doing online payment transfer. Here, I have talked about 1) using QR code for payment transaction 2) system design diagram 3) sequence of flows 4) Scaling the system Similar methods are used in system designs like cash.app, venmo, paypal and google pay. The two sequence I have discussed are Sequence 1 ------------------- Buyer and seller registers in the system Buyer goes to store and purchases item. (Stored in Buyer trans table) Seller has the transaction stored (Stored in Seller trans table) Seller shows the QR code to the Buyer generated by POS device Buyers scan the QR code through his phone’s app. Buyer enters the amount and clicks OK. Money transferred from Buyer to Seller and receipt generated. Transaction completes. Sequence 2 (Paytm method for street vendors) ------------------------------------------------------------------------------- Buyer and seller registers in the system Seller downloads the QR code and displays in front of his store. Buyer goes to store and purchases item. (Stored in Buyer trans table) Buyers scan the QR code displayed in store through his phone’s app. Buyer enters the amount and clicks OK. Money transferred from Buyer to Seller SMS notification sent to Seller and Buyer for confirmation Transaction completes. This is an amazon interview question and paytm interview question. #systemdesign. More about loadbalancer at    • System design : Why do we need Load balanc...   ------------------------------------------------------------------------------------------------ Who am I ? :   / keerthikanth