Mobile App Development for Event Ticket Sales

Developing a Mobile Application for Event Ticket Sales

The main technical pain of a ticketing app is competitive selling. When 500 people simultaneously press "Buy" for the last 10 seats, the app must correctly handle it without double bookings, freezes, or incorrect statuses. This is not a frontend task — we design the server side with pessimistic locking and queue-based reservation. The mobile client is ready for the "seat already taken" scenario with clear UX and instant feedback.

We create turnkey ticketing applications: from interactive seating maps to a controller app. Our experience in this field is 5+ years with over 20 successful projects. We guarantee fault tolerance under load and compliance with App Store Review Guidelines (Section 4.2/5.1).

Seat Reservation and Race Conditions

The standard scheme: a user selects a seat → the server creates a reservation with a TTL of 10 minutes → the user pays → the reservation is converted into a ticket. If payment is not completed within 10 minutes, the seat is released.

On the mobile client, the reservation timer is a CountDownTimer (Android) or Timer.scheduledTimer (iOS) synchronized with the server TTL. Not from the moment the button is pressed on the client, but from reservation.expiresAt from the server response. Time zone differences and device clock drift will kill the UI timer if synced incorrectly.

// Android: synchronize timer with server expiresAt
class ReservationViewModel : ViewModel() {
    private val _timeLeft = MutableStateFlow(0L)
    val timeLeft: StateFlow<Long> = _timeLeft

    fun startCountdown(expiresAt: Instant) {
        viewModelScope.launch {
            while (true) {
                val remaining = ChronoUnit.SECONDS.between(Instant.now(), expiresAt)
                if (remaining <= 0) {
                    _timeLeft.emit(0)
                    onReservationExpired()
                    break
                }
                _timeLeft.emit(remaining)
                delay(1000)
            }
        }
    }
}

When the reservation expires, we don't just show an error. We automatically suggest the nearest available seats if a real-time stream (WebSocket or SSE) supports it.

How to Avoid Double Booking?

Double booking is a classic problem with parallel requests. We solve it using SELECT FOR UPDATE in PostgreSQL or a distributed lock at the reservationId + seatId level in Redis. An alternative is ON CONFLICT DO NOTHING when inserting the reservation. On the client, we duplicate the lock: the "Buy" button is deactivated after the first press, and repeat requests are sent with a unique idempotency key. These methods reduce the likelihood of conflict by 3 times under peak loads.

Seating Map and Interactive Venue

For concert halls and theaters, an interactive seating map is needed. On iOS — UICollectionView with a custom UICollectionViewLayout or Canvas in SwiftUI for venues with non-standard geometry. On Android — Canvas + GestureDetector for pinch-to-zoom.

The map is loaded as JSON with coordinates of each seat, section, and status (available, reserved, sold, disabled). Real-time status updates — via WebSocket: as soon as someone reserves a seat, all connected clients receive { type: "seat_reserved", seatId: "A-15" }.

SVG venue maps are a popular choice for cross-platform solutions. React Native with react-native-svg or Flutter with flutter_svg + GestureDetector render SVG with tap-ability on elements.

Why is Real-Time Update Important?

Without WebSocket, a user might select a seat that is already taken. This leads to frustration and lost sales. We implement WebSocket connections with automatic reconnection (exponential backoff). As soon as a reservation changes, the client receives an event and redraws the map. For offline mode, we cache the last state and show a warning.

Electronic Tickets and Entry Validation

Each purchased ticket gets a unique UUID and a QR code generated on the server. There's no need to store a secret in the QR — just ticketId; verification is done on the server when scanned. The QR should not be a static image in a PDF — we generate it dynamically from ticketId on the client using ZXingObjC (iOS) or zxing-android-embedded, to avoid storing raster images in the database.

The controller app — a separate screen or a separate app with a scanner using AVFoundation/CameraX, POST to /tickets/{id}/validate, response: valid / already_used / invalid. We cache validated ticketId locally on the controller device in case of no internet — synchronization after connectivity is restored.

Payment Flow

Acquiring — YooKassa, CloudPayments, or Stripe. On iOS, additionally Apple Pay (PKPaymentRequest), on Android, Google Pay. For the B2B segment — invoicing by email with payment via SBP (Fast Payment System).

After payment, immediate sending of a PDF ticket via email through SendGrid/Postmark and a push notification via FCM/APNs with a deep link to the "My Tickets" screen.

How We Do It: Stack and Process

We start by analyzing your business requirements and technical constraints. Our typical stack includes PostgreSQL, Redis, Java/Kotlin on the backend, Swift/Kotlin for native mobile apps, and WebSocket for real-time updates. We follow a modular architecture to ensure scalability and maintainability.

CREATE TABLE ticket_validations (
    ticket_id UUID PRIMARY KEY,
    validated_at TIMESTAMP DEFAULT NOW()
);

Typical Errors

• Double booking. Without SELECT FOR UPDATE or distributed locking, two users could create a reservation for the same seat.
• QR on screenshot. Do not implement screenshot protection. The QR should be single-use upon validation.
• Time synchronization. Always use server-side expiresAt, not local time.

Stages and Timeline

Data model design → seating map → reservation with TTL → payment → electronic tickets → controller app → load testing (1000+ concurrent users).

6–10 weeks for a full-featured app with an interactive seating map and real-time updates. The cost is calculated individually after requirements analysis.

Get a consultation on ticketing architecture. Order development for your project — we'll make an estimate within 1 day.

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)

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.

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.