Building an e-commerce catalog inside a Telegram Mini App looks straightforward at first glance: render a grid of items in Vue 3, track selected items in local state, and call a payment gateway when the user clicks buy. However, embedded WebViews inside iOS and Android Telegram clients introduce strict constraints that ruin naive implementations.

If you rely purely on client-side state, user carts vanish every time Telegram reclaims memory or when the user toggles between chat threads. Worse, if your Vue frontend calculates the final order amount and sends that total directly to your bot backend or payment processor, malicious users can open Telegram Web Inspector, tamper with the Pinia store, and purchase high-ticket items for pennies.

In this tutorial, we will build a resilient product catalog in Vue 3 using Pinia for persisted local storage state, synchronize the interface with Telegram's native MainButton , and route checkout requests to a secure backend endpoint that verifies Telegram initData HMAC…