How to Build a Full-Cycle Mobile App for Your Online Store

A mobile app for your online store competes not with your website — it competes with OZON, Wildberries, and Rozetka. Users expect a certain UX: fast search, smooth catalog scrolling, instant checkout. Any deviation from known patterns leads to lost customers. We build e-commerce apps that match market leaders, packaged in a clear process with guaranteed results. Average mobile conversion is 2.5–3%, higher than desktop, and apps with push notifications retain 35% more users. Get a consultation and accurate project estimate — just write to us.

Why Your E-commerce Mobile App Catalog Lags and How to Fix It

The most common bottleneck is the catalog screen with images. UICollectionView on iOS or LazyVerticalGrid in Flutter stutter during scrolling if image decoding is synchronous. Solution: SDWebImage (iOS) / Coil (Android) with disk caching and prefetch via UICollectionViewDataSourcePrefetching / PagingSource. On React Native, use FlashList instead of FlatList for large lists: virtualization works better, no issues with keyExtractor and getItemLayout. FlashList outperforms FlatList by 2x in Scroll Performance tests.

Product images are the main cause of large data loads. We use WebP (25–30% smaller than JPEG at comparable quality), lazy loading, and image size matching the actual UIImageView — we don't load 2000x2000 for a 150x150 preview. This saves up to 30% bandwidth and speeds up loading.

How We Implement Search and Filters

Search input with 300ms debounce → request to search endpoint (Elasticsearch/Meilisearch on the backend). Autocomplete based on popular queries and product names. Search history stored in UserDefaults/DataStore Preferences.

Filters — a separate screen (bottom sheet or modal): category, price (RangeSlider), brand, size, color. Applying a filter does not reload the entire catalog — just updates URL query parameters and shows a skeleton loader while new results load. Active filters appear as chips above the catalog with an X for quick removal. This is the e-commerce standard; without it users get lost.

Cart and Checkout: What's Inside?

The cart syncs with the server — not just in UserDefaults. A user adds an item on phone, opens the app on tablet — same cart. Mechanism: on every change (add/remove/quantity) — PATCH /cart in the background. On opening the cart screen — GET /cart for sync.

Checkout — critical flow. Maximum steps: address → delivery → payment → confirmation. Prefill whatever we can (address from profile, saved card). Apple Pay/Google Pay — we add them by default: according to Stripe, checkout conversion is 15–20% higher with them. One-tap checkout for returning users: saved address + saved card → one confirmation screen.

Personal Account, Reviews, and Push Notifications

Order history — paginated list with status filter. Order detail page: items, delivery tracking, option to cancel or return. Tracking — either via delivery service API (CDEK, Russian Post, Nova Poshta), or a link to the site.

Push notifications for order status — mandatory: 'Your order has been shipped', 'Your order has arrived at the pickup point'. We use FCM + APNs with rich notifications (product photo in notification).

Review with photo: user uploads from gallery or camera. Upload via pre-signed S3 URL directly from device (not through the server — saves bandwidth and time). Product rating — stars + review count on card and detail page. Reviews with photos increase purchase conversion by 10%.

E-commerce Mobile App Development Process

1. Analysis and prototyping — examine business logic, target scenarios, competitors. Collect requirements for catalog, search, cart, checkout.
2. UX/UI design — create user flows in Figma, approve with client. Follow App Store and Google Play guidelines.
3. Development — parallel work on iOS and Android (or cross-platform stack). Each module covered with unit tests.
4. Backend integration — connect APIs for products, cart, orders. Use GraphQL or REST.
5. Testing — QA on real devices, performance testing, OS version compatibility.
6. Deployment to stores — upload to App Store Connect and Google Play Console, go through moderation.
7. Post-release support — monitor crash reports, update for new OS versions.

What's Included in the Result?

• Source code with comments and API documentation
• Screen schematics and user scenarios
• Access to App Store Connect and Google Play Console
• Configured push notifications and analytics (Firebase / Amplitude)
• Operations guide for your team
• 2 weeks of free post-launch support

Our experience — over 5 years in mobile development and 50+ completed e-commerce projects. With over 5 years in mobile development and more than 50 e-commerce apps delivered, we guarantee a polished product. We know how to pass App Store and Google Play moderation without unnecessary iterations. Order development and get an expert consultation — just write to us.

Timeline Estimates

MVP (catalog, search, cart, checkout with one payment method, order history): 4–8 weeks. Full-featured app with reviews, wishlists, loyalty program, tracking, and push campaigns: 2–4 months. The cost is calculated individually, but we always provide a transparent estimate before work begins. For example, an MVP development typically costs between $12,000 and $25,000 depending on features. Contact us for a free project assessment.

Cross-platform development with Flutter is 2x faster than building separate native apps, allowing you to reach both iOS and Android users in half the time. With push notifications, apps retain 35% more users than websites, and checkout conversion jumps 15–20% when Apple Pay or Google Pay is integrated.

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.