M-Pesa processes over $314 billion in transactions annually across Africa. For any business building digital products in East Africa, M-Pesa integration is not optional — it is essential. Here is how we do it at Brainstormer AI Labs. The Daraja API is M-Pesa's developer interface. It supports several transaction types: STK Push (customer-initiated), C2B (Customer to Business), B2C (Business to Customer), and B2B (Business to Business). For most e-commerce applications, STK Push is the primary integration point. Security is paramount when handling financial transactions. We implement multiple layers of protection: encrypted API credentials stored in environment variables, request signing with OAuth tokens, callback URL validation, and transaction amount verification. Error handling is where most M-Pesa integrations fail. The API can return various error codes, and network timeouts are common in African markets. We implement retry logic with exponential backoff, transaction status polling, and comprehensive logging for debugging. Testing is critical before going live. Safaricom provides a sandbox environment that mimics production behavior. We run automated tests against every possible scenario: successful payments, insufficient funds, wrong PINs, timeouts, and duplicate transactions. Our webhook architecture processes M-Pesa callbacks asynchronously. We use a queue system (Redis + Celery) to handle high-volume transaction notifications without blocking the main application thread. For reconciliation, we built a custom dashboard that compares our transaction records with M-Pesa statements. This catches discrepancies within minutes rather than days, saving our clients from revenue leakage. The result: our M-Pesa integrations process thousands of transactions daily with 99.9% uptime. Our clients trust us because we build payment systems that are secure, reliable, and optimized for the African market.