Ecommerce APIs are integral for integrating platforms, services, and apps to efficiently manage functions such as products, carts, payments, orders, and shipping, thereby accelerating development and maintaining modularity. Various production-ready APIs like Shopify Admin API, BigCommerce API, Stripe, WooCommerce REST API, JD.com Open API, and Magento API offer different capabilities and limitations, such as rate limits and integration complexities. Building a robust mobile ecommerce app involves implementing a comprehensive API stack to ensure speed, scalability, and seamless user experience, which includes secure authentication, product and inventory management, cart and checkout processes, order fulfillment, and real-time engagement through platforms like PubNub. The architecture should emphasize data normalization, caching, error handling, secure payment integration, CI/CD, and monitoring to enhance app resilience and performance. Migrating an ecommerce platform requires careful evaluation of checkout API flexibility, catalog and inventory API scalability, order management maturity, performance, rate limits, and extensibility to ensure a smooth transition and future-proof the technology stack.