DeFi protocol integration into a mobile wallet

Native DeFi protocol integration into a mobile wallet

A wallet developer wants to add token swaps via Uniswap. The easy route is a WebView with the official dApp, but that gives a third-party UI, loss of gas control, and security limitations. Native integration solves this: direct smart contract calls, local signing, customization. We connect your mobile wallet directly with DeFi protocols: calling Uniswap Router, Aave LendingPool, Compound cToken methods. The interface is built on top of JSON ABI, transactions are signed locally, data is read via RPC without intermediaries. This is not a WebView dApp—it's full smart contract interaction. Our proven experience: over 5 years in mobile development, 10+ successful DeFi integrations, 30+ blockchain projects. Native integration is twice as secure as WebView against phishing due to local signing via Secure Enclave. Get a consultation—we'll assess your project with a guaranteed response within 24 hours.

ABI-first approach

Each DeFi protocol is a set of smart contracts with a public ABI. The app's task: encode a call by ABI, sign the transaction, send it. For EVM, libraries like web3swift (iOS) or web3j (Android) provide EthereumContract for dynamic ABI work.

// iOS — calling Uniswap V3 QuoterV2 to get a quote
let quoterABI = try! EthereumContract(json: quoterV2ABI)
let result = try await quoterABI.read(
    "quoteExactInputSingle",
    parameters: [tokenIn, tokenOut, fee, amountIn, sqrtPriceLimitX96] as [AnyObject],
    transactionOptions: nil
)

For Solana and its protocols (Raydium, Orca, Jupiter), Anchor SDK generates IDL (Interface Definition Language), analogous to ABI. SolanaSwift + Anchor allows typed program instruction calls.

Uniswap V3: swap via Router

Uniswap V3 is the most intricate popular protocol for mobile integration. SwapRouter02 (0x68b3465833fb72A70ecDF485E0e4C7bD8665Fc45) accepts ExactInputSingleParams:

// Android — encoding exactInputSingle call
val function = Function(
    "exactInputSingle",
    listOf(
        DynamicStruct(
            Address(tokenIn),
            Address(tokenOut),
            Uint24(fee),         // 500, 3000, or 10000
            Address(recipient),
            Uint256(amountIn),
            Uint256(amountOutMinimum), // with slippage considered
            Uint256(BigInteger.ZERO)   // sqrtPriceLimitX96
        )
    ),
    listOf(Uint256())
)
val encodedData = FunctionEncoder.encode(function)

Before the swap, an approve on the SwapRouter is needed: ERC-20 approve(routerAddress, amountIn). Without it, the swap transaction will revert with TransferHelper: TRANSFER_FROM_FAILED.

For quotes, use QuoterV2.quoteExactInputSingle (read-only, off-chain). Never use the on-chain Quoter for real-time UI updates — it's an eth_call that loads the node.

Aave V3: supply and borrow

The Aave Pool (0x87870Bca3F3fD6335C3F4ce8392D69350B4fA4E2 on Mainnet) accepts supply(asset, amount, onBehalfOf, referralCode). The logic:

1. Approve Pool for the token amount.
2. Call supply — get aToken in return.
3. For borrowing, check getUserAccountData and ensure healthFactor > 1.5 before recommending a loan amount.

A healthFactor below 1.0 means liquidation. The mobile app should display the health factor in real time and warn when it approaches 1.1.

How to ensure reliable transaction signing?

To protect against phishing, we use EIP-712 (Ethereum Typed Data). All transaction data is displayed to the user in a readable format. Private keys are stored in Keychain (iOS) / Android Keystore. Signing is done locally, no internet required. Additionally, biometric authentication can be used for confirmation.

WalletConnect for dApp browser

If the wallet wants to support connecting to external dApps via a mobile browser, we use the WalletConnect v2 SDK (com.walletconnect:walletkit for Android, WalletConnectSwift for iOS). The protocol establishes an encrypted channel between the dApp and the wallet. The wallet receives signing requests, shows the user transaction details, signs locally, and returns the signed hex.

Why integrate DeFi natively instead of through WebView?

Native integration gives full control over transactions, reduces gas, and improves user experience.

State management and protocol data caching

DeFi data updates with every block. Uniswap pool price, Aave interest rates are read via Multicall3 every 12–15 seconds. Store in reactive state (Combine on iOS, Flow/StateFlow on Android). On RPC error, show graceful degradation: display last known data with a timestamp.

Common issues

Slippage tolerance must not be hardcoded. 0.5% works for stablecoin pairs, 1–3% for volatile ones. Too low slippage causes constant transaction reverts on volatile markets; too high invites sandwich attacks.

Gas estimation for DeFi operations can be off: Uniswap V3 with some routes consumes 200k–500k gas. Multiply estimation by 1.3, not 1.1.

Process

1. Analysis: define protocol list, collect ABI/IDL.
2. Design: ABI layer architecture, reactive state, error handling.
3. Implementation: code swap, supply, borrow functions, integrate WalletConnect.
4. Testing: on testnet (Goerli, Sepolia, Mumbai), check edge cases.
5. Deployment: publish to App Store / Google Play, monitor.

What's included

• ABI integration documentation with code examples
• Test cases for all scenarios (success, revert, gas errors)
• Training your team on web3swift/web3j libraries
• One month post-release support guarantee (bug fixes, consultations)

Contact us — we'll assess your project with a guaranteed response within 24 hours. With 5+ years of experience and 30+ blockchain projects, we are a trusted partner.

Timeline: 1–3 months depending on the protocol set. One protocol (e.g., only Uniswap V3 swap) takes 1–2 weeks including testnet testing. A full DeFi hub with Uniswap + Aave + Compound takes 2–3 months. Cost starts at $15,000.

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.