Customer purchasing and payment system use case diagram maps interactions between Customer, Cashier, and Manager roles across product selection, payment processing, and inventory management. The sequence flows from customer product selection and payment through cashier-driven purchase processing, payment receipt, and sales record updates, while managers oversee sales reporting and inventory control. This use case architecture demonstrates role-based responsibility separation and end-to-end transaction lifecycle in retail environments. Fork and customize this diagram on Diagrams.so to align with your specific POS requirements, payment gateways, or multi-location inventory systems. The model supports extension to include payment processors, barcode scanning, or real-time stock synchronization.