Implementing Futures Trading in a Cryptocurrency Exchange Mobile App

Implementing Futures Trading in a Cryptocurrency Exchange Mobile App

We develop mobile modules for futures trading — with perpetual contracts, leverage up to 125x, and a funding rate mechanism. Unlike spot trading, there is no real asset, only a contract on the price difference. This imposes fundamentally different requirements on the interface: Mark Price, Funding Rate, Liquidation Price, unrealized/realized PnL, and margin mode — everything must update in real time. Below is how we solve these challenges.

Why Futures Trading Is More Complex Than Spot on Mobile Devices

The spot screen shows price, chart, and order form. The futures screen adds margin indicators, liquidation, funding, and Long/Short switching. All data must be accessible without scrolling and confusion. A mistake in displaying the Liquidation Price can lead to loss of funds. Therefore, we use proven architectural solutions: WebSocket for streams, local caching of Mark Price, and a liquidation calculation formula that accounts for Cross/Isolated margin mode.

Perpetual Futures: Key Concepts for the UI

Mark Price — the index price calculated by the exchange based on a weighted average of several spot markets and the funding premium. It is used to compute PnL and liquidation — not the Last Price. The difference between Mark and Last can reach 0.5–2% during high volatility. In the UI, we show both values.

Funding Rate — the rate that longs pay to shorts (or vice versa) every 8 hours. When the deviation is significant, the rate can be 0.1% every 8 hours (~0.3% per day). We display the Funding Rate and a countdown timer until the next payment in the position card.

Leverage on futures changes dynamically via a slider or input field. The maximum leverage depends on position size: for example, on Binance, 125x is available only for positions up to 50,000 USDT.

Liquidation Price: Calculation for Futures

Formula for USDM perpetual (Binance Futures), LONG position:

LiquidationPrice = EntryPrice × (1 - InitialMarginRate + MaintenanceMarginRate)

where InitialMarginRate = 1 / Leverage.

// Android — liquidation price for perpetual futures LONG
fun calcLiqPriceLong(
    entryPrice: BigDecimal,
    leverage: Int,
    mmRate: BigDecimal = BigDecimal("0.005") // Maintenance Margin Rate
): BigDecimal {
    val imr = BigDecimal.ONE.divide(BigDecimal(leverage), 8, RoundingMode.HALF_UP)
    return entryPrice.multiply(BigDecimal.ONE.subtract(imr).add(mmRate))
        .setScale(2, RoundingMode.HALF_UP)
}

For positions with averaging, the Entry Price is recalculated as a weighted average, and the Liquidation Price is updated. In Cross Margin mode, the entire balance is considered.

How to Ensure Real Position Safety with TP/SL

In futures, Take Profit and Stop Loss are set as attributes of a position, not separate orders. Binance Futures API: POST /fapi/v1/order with parameters reduceOnly=true, or creating TP/SL via closePosition=true. It is important to use workingType: MARK_PRICE — TP/SL triggers based on Mark Price, protecting against false triggers (wick hunting). We explain this to the user in a tooltip.

// iOS — creating TP/SL for a futures position
struct FuturesTpSlRequest: Codable {
    let symbol: String
    let side: String          // opposite to the current position
    let type: String          // TAKE_PROFIT_MARKET or STOP_MARKET
    let stopPrice: String
    let closePosition: String // "true"
    let workingType: String   // MARK_PRICE or CONTRACT_PRICE
    let timeInForce: String   // GTE_GTC
}

According to Binance API Reference, this approach eliminates accidental liquidations.

UI of the Trading Screen: What We Do Differently

The futures trading screen is overloaded with data. Our mobile structure:

• Top: Mark Price (large), Last Price, Funding Rate + Countdown, 24h Change
• Center: candlestick chart (TradingView Lightweight Charts in WebView) with timeframe switching
• Bottom: tabs "Position" / "Open Orders" / "History" + order form

The order form is a Bottom Sheet with Long/Short tabs. Fields: Leverage (slider), Price (limit orders), Size (in contracts or USDT), margin mode Cross/Isolated.

Comparison of UI Approaches: Spot vs Futures

Our Experience and Quality Guarantees

We have been developing mobile exchange applications for 5+ years, completing over 10 projects for crypto exchanges and brokers. Every module undergoes code review, load testing, and compliance checks with App Store / Google Play guidelines. We provide full documentation and support during integration.

What's Included in the Work

• Architectural design of the module (data flow diagrams, WebSocket nodes)
• Development of UI components for iOS (Swift/SwiftUI) and Android (Kotlin/Jetpack Compose)
• Integration with exchange API (REST + WebSocket)
• Configuration of push notifications (APNs/FCM) for liquidation risks
• Testing: unit tests, UI tests, testing on emulators and real devices
• Documentation for developers and end users
• Assistance with publishing to App Store / Google Play

Timeline

MVP of the futures module (perpetual, Long/Short, TP/SL):

Total: 4–6 weeks. Full module with Multi-asset Mode, Portfolio Margin, hedge mode — 3 months.

We will evaluate your project for free — contact us for a consultation. Let us know, and we will explain how to implement futures trading turnkey in your app.

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.