Shipping an e-commerce storefront inside a Telegram Mini App using Next.js App Router seems straightforward until untrusted client state compromises your checkout process. Front-end developers frequently rely on window.Telegram.WebApp.initDataUnsafe to identify the user and send cart totals directly from the client to an API route. Because initDataUnsafe can be mutated by anyone opening your app in a standard browser or using browser developer tools, accepting unverified user IDs or total prices from the front end allows users to modify invoice amounts, impersonate other customer accounts, or execute unverified orders.

Building a robust Telegram Mini App shop requires verifying the raw initData payload using an HMAC-SHA256 signature on the server, calculating cart prices strictly from stored backend database values, controlling Telegram's native MainButton across React render lifecycles, and accounting for renderer discrepancies between iOS WebViews and Telegram Desktop.

Validating Telegram initData in…