How SellerVai Built a Webhook Architecture to Handle Flash Sale Message Surges

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SellerVai is a Bangladesh-based automated sales platform that manages customer orders via WhatsApp, Facebook Messenger, and Telegram in Bengali and Banglish. The platform addresses a common South and Southeast Asian e-commerce pattern where purchases happen entirely through chat rather than traditional online storefronts. A key engineering challenge was preventing message loss and duplication caused by Meta's webhook retry mechanism when responses are delayed. The team solved this by separating message receipt from processing — the webhook only verifies and acknowledges delivery, while a Redis-backed queue handles all conversation logic asynchronously. During a promotional campaign that drove 15 times normal traffic, the architecture kept webhook endpoints responsive and processed the backlog without duplicate orders or missed messages.

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