Turnkey mPOS Payment App Development

Imagine this: a courier arrives with an order, but the terminal battery is dead. Or a customer wants to pay by card, but the reader won't connect after the screen locks. Such errors cost businesses significant revenue — according to statistics, one in five mPOS terminals loses connection during a transaction, representing 20% of lost income. Our mobile development team, with 8 years of fintech experience (15+ projects), solves these problems systematically: we design mPOS apps that reliably accept payments even in challenging scenarios. We build turnkey mPOS solutions: from SDK selection and reader integration to fiscalization and store publication. We'll evaluate your project in 1–2 days — contact us for a consultation.

Ensuring Stable Bluetooth Connection with the Reader

Bluetooth connection is the primary source of mPOS issues: the reader disconnects mid-transaction, the phone can't find it after screen lock, the battery dies. We implement reconnect logic with automatic search and reconnection to the last used reader. We use CoreBluetooth (iOS) or BluetoothAdapter (Android) with constant scanning, automatic reconnection on drop, and connection state notifications. Stripe Terminal SDK handles reconnection itself, reducing development time by 30–40% compared to implementing the EMV stack and Bluetooth connection from scratch. We test with specific readers under interference conditions.

Hardware and SDK

Stripe Terminal SDK (stripe-terminal-ios, stripe-terminal-android) is the most documented choice for new projects. It supports multiple reader types and handles EMV transactions, online and offline mode. According to Stripe, 70% of users prefer contactless payments, so NFC support is mandatory. Integrating Stripe Terminal SDK reduces development time by 30–40% compared to building from scratch. Detailed documentation.

Why Apple Tap to Pay is Changing the mPOS Market

Apple Tap to Pay (iPhone with modern iOS) accepts contactless cards via iPhone's NFC without an external reader. Requires a Partner SDK from an Apple-approved PSP (Stripe, Adyen, Checkout.com support it). Integration via the ProximityReader framework. This changes the mPOS market — no reader needed. Reduces hardware costs up to 3x compared to buying a separate reader. For Android, similar functionality is available via HCE, but requires payment system certification.

EMV and NFC

Card transactions follow international standards — EMV (Chip & PIN, Chip & Sign) and contactless (NFC). Stripe Terminal SDK handles the full EMV dialog with the chip — the developer doesn't need to implement ISO 7816 APDU commands manually. NFC on the device without a reader: iOS only supports Apple Pay via PassKit; Android HCE (Host Card Emulation) allows accepting contactless Visa/MC via NFC, but requires certification.

What to Do When There's No Network?

A courier in an underground passage — no network. The transaction must complete. Stripe Terminal supports offline mode: the transaction is authorized locally on the device, queued, and synced when network is restored. The offline amount limit is configurable. Chargeback risk with offline transactions is accepted by the business knowingly.

Receipts: Electronic and Printed

Electronic receipt — SMS or email. Printed receipt — integration with a Bluetooth printer (Star Micronics TSP143, Epson TM-P20). Star Bluetooth SDK (iOS/Android) — the printer works as a CBPeripheral, commands in StarIO format. Fiscal receipt in Russia — integration with OFD through FN/SKNO. ATOL, Evotor, Комтет are popular solutions. Mobile fiscal registers (ATOL 91F, SHTRIKH-MPAY-F) connect via Bluetooth, using the manufacturer's SDK.

Main Screen and UX

For a cashier using the mPOS app, speed is paramount. Main screen: amount input field (digital keypad, large font) + "Accept Payment" button. Product catalog is optional for those managing inventory. Shifts: opening/closing cash register shifts with Z-report. Operator authorization via PIN code. Transaction history with search and filter by period. Refunds — partial and full, confirmed with a manager PIN.

What's Included

• Architecture documentation and API specification
• Terminal SDK integration and Bluetooth connection
• Payment flow (EMV + contactless + NFC)
• Receipts (electronic and printed)
• Fiscalization (for Russia/Belarus)
• Testing with real readers
• PSP certification and publication on App Store / Google Play
• Technical support for 2 months after release

Tech Stack

Native Swift + Kotlin — preferred for mPOS due to direct access to CoreBluetooth/BluetoothAdapter, ProximityReader, and hardware interfaces. React Native with native modules for Bluetooth and Terminal SDK is a viable option for cross-platform requirements. Stripe Terminal SDK vs. proprietary reader SDKs: Stripe wins on multi-reader support and built-in offline mode, reducing development time by 30-40%.

Process

Reader and PSP selection → Terminal SDK integration → Bluetooth connection and reconnect → Payment flow (EMV + contactless) → Receipts (electronic and printed) → Fiscal integration → Testing with real equipment → PSP certification → Publication.

Timeline Estimates

Basic mPOS (amount input, payment via Stripe Terminal, electronic receipt): 3–4 weeks. Full-featured app with catalog, shifts, refunds, fiscal register, and Bluetooth printer: 2–3 months. Cost is determined after requirements analysis. Our engineers support the project at every stage — from idea to release and beyond. Contact us for a consultation on your mPOS project. Request an individual cost estimate.

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.