esimapp — travel eSIM store

The product

esimapp.io sells prepaid travel eSIM data for 200+ destinations. A traveller picks a country or region, sees every plan with its total price and its price per GB (cheapest first), pays, and gets the eSIM — QR code, activation code and ICCID — on screen and by email within minutes. No account is needed to buy; accounts are optional for people who come back.

My role

It’s my own product. I designed it, wrote the product and design specs, built the whole stack and run it in production — about 590 of its 600+ commits are mine.

What I built

• Zero-touch fulfilment. The eSIM is ordered from the wholesale API only after the payment is confirmed on the server, then delivered automatically when the provisioning webhook arrives.
• Payments you can’t double-charge. Hosted checkout with card, Apple Pay and Google Pay; the webhook is re-checked against the payment provider’s API, a second payment for the same order is refunded automatically, and the eSIM order is keyed so a retry can never buy twice.
• Automatic refunds. If provisioning fails after payment, the customer is refunded in full and I get an alert — no manual step.
• Optional accounts. Email and password, Google or Telegram sign-in, guarded by Cloudflare Turnstile; a verified email claims that address’s earlier guest orders.
• A store-credit wallet. Account holders can top up by card or crypto and pay from their balance.
• An admin back office. Orders, packages, pricing with a default markup and per-package overrides, the email log, background jobs and a sales switch, with admin and read-only support roles.
• Built for a phone in a hurry. Mobile-first, pre-rendered pages, a performance budget, and every page on translation keys so more languages can follow.

Hard problems

• Two webhooks, one order. Payment and provisioning arrive from two different services, in any order and sometimes twice; every handler is idempotent so each order ends either delivered or refunded, exactly once.
• Shipping fast without breaking things. A test suite of 4,500+ tests, a private staging copy and a scripted deploy with one-command rollback let me go from first commit to a live store in about four weeks.