A user opens the app, types a departure station, and sees the ticket price for tomorrow. One click — a car diagram with occupied seats. Another click — a PDF ticket with a QR code that works offline. That's what a mobile app for railway tickets looks like, and we develop such solutions. With 30+ projects and experience working with transport APIs: Tutu.ru, UFS, Express-3. Here's how to do it right.
What Problems We Solve
Integration with monolithic APIs. Express-3 is a legacy system from Russian Railways with SOAP/XML; it's slow under peak loads. Aggregators like Tutu.ru provide JSON in ~200 ms but require caching and error handling. We build a middleware layer: retries with exponential backoff, fallback to UFS on timeouts.
Seat selection in a car. Compartment, open-plan, SV — each has its own layout. Data arrives as an array of seats with coordinates. Deserialization of heavy responses (up to 500 KB) is a bottleneck. On iOS we use DispatchQueue.global(qos: .userInitiated), on Android Dispatchers.IO.
Offline access to tickets. After payment, the QR code of the itinerary receipt is stored locally. On iOS — PDFKit, on Android — PdfRenderer. Push notifications via FCM/APNs handle schedule changes.
How We Develop a Railway Ticket App
The process — from analysis to deployment. We use a modern stack: Swift 5.9 + SwiftUI (iOS) / Kotlin + Jetpack Compose (Android) or Flutter 3.x for cross-platform.
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Analysis and prototype. We define the API (Tutu.ru / UFS / Ticketcloud), draw screens. We document refund logic and dynamic pricing.
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Design. We develop data schemas, routing, error handling. We configure code signing and provisioning profiles.
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Implementation. We write modules: search, seat selection, payment (StoreKit 2 / Google Billing 6), ticket storage. We embed deep linking (Universal Links / App Links) for transitioning from push notifications.
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Testing. TestFlight / Firebase App Distribution. We test scenarios: interrupted payment, refund, weak signal.
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Deployment. We publish to App Store and Google Play. We comply with App Store Review Guidelines and Google Play Policy.
Case in point: for one client, integration with Tutu.ru API took 2 weeks. The issue was that their endpoint didn't support batch requests. We parallelized calls using Combine (iOS) and coroutines (Android). Response time for 10 stations — 800 ms instead of 2 seconds.
Why Is Offline Ticket Access Critical?
The app must work in metro, tunnels, and areas with poor coverage. The QR code of the itinerary receipt is generated on the server but stored locally in PDF. For rendering, we use PDFKit on iOS and PdfRenderer on Android. This ensures the conductor can scan the ticket even without internet. Additionally, we sign the code via push notifications: when the schedule changes, FCM/APNs deliver a short signal, and the app updates cached data on the next connection.
Comparison of Aggregator APIs
| API |
Format |
Speed |
Refunds |
Dynamic Pricing |
| Tutu.ru |
JSON |
~200 ms |
No direct support |
Yes |
| UFS |
XML |
~400 ms |
Yes |
Yes |
| Ticketcloud |
JSON |
~300 ms |
Yes, 2% commission |
No |
Tutu.ru is 2x faster — critical for searches with 10+ requests.
Which Payment Methods Are Supported?
SBP (instant, no commission), YooKassa, PSB. Apple Pay via PKPaymentRequest, Google Pay via PaymentsClient. Without these, conversion drops by 20%. The choice of payment provider affects confirmation speed: SBP credits funds in seconds, while card transactions can take up to 3 minutes.
Comparison of Payment Methods
| Method |
User Commission |
Speed |
Notes |
| SBP |
0% |
Instant |
No amount limit |
| YooKassa |
0-2% |
Up to 1 minute |
Supports cards and SBP |
| Apple Pay |
0% |
1-2 seconds |
Requires Face ID / Touch ID |
| Google Pay |
0% |
1-2 seconds |
Requires biometrics |
How Does Dynamic Pricing Work?
In Express-3, the price rises as seats decrease. We show the dynamics in the train card: if seats are below a certain threshold, we highlight the price. For accurate calculation, we use Tutu.ru or UFS API with 5-minute caching.
And Ticket Refund — How Does It Work?
Refund is a separate API call. Penalties: up to 8 hours before departure — full refund minus fee; less than 8 hours — 50% of the price. We do not implement calculation logic on the client side.
What Is Included in Turnkey Development
- Integration documentation with the chosen API
- Source code of the app (iOS/Android)
- Build and publication to App Store and Google Play
- Test access via TestFlight/Firebase
- Client team training (2 hours online)
- 1 month post-release support
Why Choose Us
Experience with transport APIs for many years, completed 30+ projects. Certified iOS and Android developers. We guarantee compliance with App Store Review Guidelines and Google Play Policy.
Timeframes and Cost
6–8 weeks for an app with search, seat selection, payment, refund, and trip history via an aggregator API. Under tight deadlines, we can deliver in 5 weeks if the API is already chosen. Cost is calculated individually. Get a consultation — we'll evaluate your project within 1 day. Contact us to discuss details.
Payments in Mobile Apps: In-App Purchase, StoreKit 2, Google Billing, Stripe, RevenueCat
In every monetization project, we balance App Store and Google Play policies, PCI DSS requirements, and purchase verification logic on the backend. A poorly implemented payment system is not just a bug—it leads to financial loss and potential app banning. Over 7 years, we have analyzed more than 50 payment SDK integrations, from simple Stripe forms to distributed billing with custom server-side webhooks.
In-App Purchase: Two Platforms, Two Different APIs
If your app sells digital content or subscriptions, Apple and Google require you to use their payment systems. This is non-negotiable: violating App Store rule 3.1.1 or Google Play Developer Policy results in app removal. Physical goods and offline services are a different story.
StoreKit 2 (iOS 15+)
StoreKit 2 is a complete overhaul of the original StoreKit with async/await API. Product.products(for:), product.purchase(), Transaction.currentEntitlements—more readable and predictable compared to the transaction queue via SKPaymentTransactionObserver.
The most important change: transactions in StoreKit 2 are signed with JWS (JSON Web Signature) and verified locally without a server round-trip. Transaction.verificationResult returns .verified(Transaction) or .unverified(Transaction, VerificationError). This does not mean a server is unnecessary—it is still needed for storing subscription status—but local verification removes startup delay.
StoreKit.AppTransaction verifies the actual app download from the App Store. Required for paid downloads or non-renewing purchases.
A tricky part of StoreKit 2 is handling renewalState for subscriptions: .subscribed, .expired, .inBillingRetryPeriod, .inGracePeriod, .revoked. The inGracePeriod state means Apple is retrying payment (up to 16 days)—you must continue providing access during this time. Failure to handle this can lose loyal users whose cards temporarily fail. Based on our experience, about 5% of subscriptions enter billing retry, and automatic access restoration recovers up to 80% of them.
Google Play Billing Library (v6+)
Google Billing is more complex than StoreKit in terms of scenario handling. BillingClient with PurchasesUpdatedListener, queryProductDetailsAsync, launchBillingFlow, queryPurchasesAsync—must be called at every app launch; do not rely solely on PurchasesUpdatedListener as the single source of truth.
Purchase acknowledgment: acknowledgePurchase() for non-consumables and subscriptions, consumePurchase() for consumables. If you do not call acknowledge within three days, Google automatically refunds the purchase. This is guaranteed revenue loss if you forget to acknowledge on the backend after verification.
ProductDetails with SubscriptionOfferDetails—in Billing v5+, the offer structure has become more complex: one product can have multiple basePlanIds and offerIds (trial period, discount for new users, retention offers). BillingFlowParams.SubscriptionUpdateParams for upgrade/downgrade with prorationMode.
Why Is Server-Side Verification Mandatory?
Never trust only client-side code when unlocking paid content. Client-side verification can be bypassed by modifying the app.
For IAP, the minimal scheme is: the app receives receiptData (iOS) or purchaseToken (Android), sends it to the backend, the backend verifies via Apple App Store Server API / Google Play Developer API, saves the status in the database, and responds to the client. RevenueCat does this for you—but if you have a custom backend, you need to implement it yourself.
Webhooks are more important than they seem. Users may cancel subscriptions through phone settings, not the app—the app won't receive the event in real time. Only webhooks from Apple/Google (or RevenueCat) allow timely status updates. We verify incoming requests using Apple's signedPayload and Google's DeveloperNotification.
How Does RevenueCat Simplify Integration?
Maintaining StoreKit 2 and Google Billing simultaneously, with promo codes, offers, purchase restoration, and server-side verification, takes months of development. RevenueCat handles most of this layer.
RevenueCat is not just a payment SDK. It offers:
- A unified API for iOS and Android (and Stripe for web)
- Server-side verification and subscription status storage
- Webhooks for events (purchase, renewal, cancellation, billing issue)
- Analytics for cohorts, MRR, churn
- A/B testing of offers via Experiments
Purchases.configure(withAPIKey:) at startup, Purchases.shared.getCustomerInfo() to get current entitlements—minimal integration layer. Purchases.shared.purchase(package:) instead of directly calling StoreKit/Billing.
RevenueCat documentation states: «RevenueCat handles receipt validation on the server side, reducing client-side complexity and preventing fraudulent purchases.»
Limitations of RevenueCat: it is paid (free up to $2.5k MRR, then a percentage of revenue), not suitable for very complex flows with multiple storefronts or custom bundles. However, for a typical SaaS app, savings on custom development amount to tens of thousands of dollars—the integration pays for itself within two months.
Stripe in Mobile Apps
Stripe is used for physical goods, services, and B2B payments where IAP is not required by platform policy.
Stripe iOS SDK and Android SDK—PaymentSheet for ready-made payment UI, PaymentSheetFlowController for custom UI with saved cards. Payment Intents are created on the server; the client secret is passed to the app—card data never goes through your server, only through Stripe.
Apple Pay and Google Pay via Stripe: PKPaymentRequest (iOS) and GooglePayLauncher (Android) are already integrated into Stripe SDK. Apple Pay conversion rates are 1.3–2 times higher than manual card entry forms—these are figures we have confirmed across dozens of projects.
Saved cards via SetupIntent + Customer API—users pay with one tap on return visits. Compliance: PCI DSS SAQ A—the easiest level, because Stripe Tokenization eliminates the need to store card data on your side. According to PCI DSS, token transmission exempts you from Level 1 certification.
3DS2 (Strong Customer Authentication) is mandatory for payments in the EU under PSD2. Stripe handles it automatically via PaymentIntent.confirmPayment, but you need to correctly handle the .requiresAction status and return the user to the appropriate screen after authentication.
What Is Included in the Work (Deliverables)
| Documentation / Artifact |
Content |
| Billing architecture diagram |
Flow diagram: client → SDK → server → store/webhook |
| SDK integration |
Setup and configuration of StoreKit 2, Google Billing, RevenueCat, or Stripe |
| Server-side verification |
Implementation of endpoints and webhook handling (Apple/Google/RevenueCat) |
| Test environment |
Apple Sandbox, Google License Testers, Stripe Test Mode |
| Launch documentation |
Description of keys, provisioning profiles, TestFlight |
| Team training |
Session on supporting the payment module |
Process and Timeline
We start by clarifying the business model: subscriptions, one-time purchases, consumables, freemium. The architecture depends on this. Testing IAP requires Sandbox accounts (Apple) and License Testers (Google)—this is a separate environment setup.
Apple's Sandbox behaves differently from production: subscriptions renew every 5 minutes instead of monthly, inGracePeriod works differently. It is essential to test scenarios: trial expiration, cancellation, billing retry, refund.
| Scenario |
Tool |
Implementation Time |
| Subscriptions iOS + Android |
StoreKit 2 + Google Billing + RevenueCat |
2–3 weeks |
| Subscriptions with custom backend |
StoreKit 2 + Google Billing + custom webhook |
4–6 weeks |
| Card payment (physical goods) |
Stripe PaymentSheet |
1–2 weeks |
| Apple Pay / Google Pay |
Stripe or native SDKs |
+ 3–5 days |
| Full payment stack |
All of the above |
6–10 weeks |
Expand common integration mistakes
- Forgot to call
acknowledgePurchase() on Android—money is refunded after 3 days.
- Did not handle
inGracePeriod—loyal users are blocked from access.
- Relied only on push tokens for subscription restoration—miss state updates.
- Used production keys in TestFlight—real charges occur.
The cost is calculated individually based on the set of tools and complexity of server-side logic. On average, we fit within a budget for a typical integration, but the savings from preventing errors and churn offset this investment within a few months.
Get a consultation for your project—contact us. We will help you choose the optimal payment architecture that passes store reviews and does not break under peak loads.
