The development of digital technology encourages businesses to adopt e-commerce systems to expand market reach and improve transaction process management. King Audio Bandung still faces limitations in its sales activities, particularly in transaction processing, data management, payment, shipping, returns, and reporting, which were previously conducted conventionally. This study aims to develop a web-based e-commerce system using the Prototype method to integrate the sales business processes end-to-end. The study employed a descriptive approach with an action research strategy. Data were collected through observation, interviews, and documentation to identify system requirements and existing business processes. System development involved requirements identification, prototype design, evaluation and refinement, implementation, and testing. The developed system provides functions for product management, ordering, payment, shipping, returns, and reporting. Functional testing was conducted using Black Box Testing involving 114 test cases, with all 114 cases receiving an ACCEPTED result, resulting in a 100% success rate (114/114). The results demonstrate that the developed system can integrate the main transaction processes with after-sales activities within a single web-based system. The main contribution of this study is the integration of e-commerce business processes covering products, orders, payments, shipping, returns, and reporting, supported by comprehensive functional testing.