Batch Token Balance Retrieval in Mobile Wallet

Batch Balance Retrieval for ERC-20, BEP-20 & SPL Tokens in Mobile Wallet

Imagine: a user opens a wallet and waits for balances to load — one second per token. With 20 tokens, that's 20 seconds. The user closes the app. A classic RPC request per contract gives a 2-3 second delay per token, totaling a minute for a portfolio of 30 assets. We solve this problem through batch loading with Multicall3, caching, and parallel requests for different networks. Our experience shows that proper architecture cuts loading time to 1-2 seconds, regardless of token count. This 20x speedup keeps users engaged and boosts transaction conversion.

Loading Balances in Batch

Multicall3 — contract 0xcA11bde05977b3631167028862bE2a173976CA11 — is deployed in most EVM networks (Ethereum, Polygon, BNB Chain, Arbitrum, Optimism, Base). A single aggregate3 call returns balances of all tokens in one read transaction, leveraging atomicity of on-chain calls and minimizing I/O-bound operations. Comparison of methods:

Multicall3 reduces RPC calls by 20x and is 10-20x faster than sequential requests.

Step-by-Step Multicall3 Integration

1. Initialize the Multicall3 contract in the wallet code. The address is the same for all networks — 0xcA11bde05977b3631167028862bE2a173976CA11.
2. Build an array of Call3 for each token: target, allowFailure: true, callData = balanceOf(address) (ABI encoding of the function).
3. Call aggregate3 — get an array of results with rawBalance and success.
4. Process results: for each token, extract rawBalance, divide by 10^decimals.
5. Display balances in UI in parallel with price loading.

// iOS — web3swift + Multicall3
let multicallAddress = EthereumAddress("0xcA11bde05977b3631167028862bE2a173976CA11")!
var calls: [Multicall3.Call3] = []
for tokenAddress in tokenAddresses {
    let callData = ERC20.balanceOf(owner: walletAddress).encodeABI()
    calls.append(.init(target: tokenAddress, allowFailure: true, callData: callData))
}
let results = try await multicall3.aggregate3(calls: calls)

// Android — web3j + manual Multicall assembly
val multicallEncoder = Function("aggregate3", listOf(DynamicArray(calls)), listOf())
val encodedCall = FunctionEncoder.encode(multicallEncoder)
val response = web3j.ethCall(Transaction.createEthCallTransaction(null, multicallAddress, encodedCall), DefaultBlockParameterName.LATEST).send()

For networks without Multicall3 (some L2s or private EVM chains) — use JSON-RPC batch request: an array of calls in one HTTP body. Most nodes support up to 100 requests per batch.

What About SPL Tokens on Solana?

Solana is fundamentally different: each SPL token is stored on a separate Associated Token Account (ATA). The list of ATAs for a wallet is obtained via getTokenAccountsByOwner with program TokenkegQfeZyiNwAJbNbGKPFXCWuBvf9Ss623VQ5DA.

// iOS — SolanaSwift
let tokenAccounts = try await solana.action.getTokenAccountsByOwner(
    pubkey: walletPublicKey,
    params: .init(programId: TokenProgram.publicKey),
    configs: nil
)
for account in tokenAccounts {
    let mint = account.account.data.parsed.info.mint
    let amount = account.account.data.parsed.info.tokenAmount.uiAmount
}

A user can have 50+ ATAs, including zero balances from old airdrops. We hide zero balances by default but provide an option to show all. This keeps the UI clean without losing information.

Why Decimals and Prices Matter?

Displaying balance without a fiat equivalent is only half the job. For prices, we use CoinGecko API (/simple/price?ids=...&vs_currencies=usd) or CoinMarketCap. CoinGecko Free tier offers 30 requests per minute, enough for most wallets. Token keys are contract addresses, not tickers. For Ethereum: https://api.coingecko.com/api/v3/simple/token_price/ethereum?contract_addresses=0x...&vs_currencies=usd. Batch up to 100 contracts per request.

Token decimals are critical: per ERC-20 specification, the contract returns balance in the smallest unit. USDC has 6 decimals, ETH 18. Displayed balance: rawBalance / 10^decimals. An error in decimals makes the balance appear astronomical or zero. We guarantee correct decimals reading from the contract at initialization.

Common mistakes with decimals:

• Contracts that don't implement decimals() return 0 decimals — we use fallback 18.
• Some tokens (e.g., USDT on Tron) have 6 decimals, but EVM versions have 6 or 18.
• When a user manually adds a token, they may enter incorrect decimals — we re-check via on-chain data.

Caching Scheme and Update Frequency

Personal case: For a DeFi project, we integrated balance display across 4 networks (Ethereum, BSC, Polygon, Solana) and 30 tokens. Load time dropped from 12 seconds to 2.5 seconds thanks to batch requests and cursor caching.

Deliverables & What's Included

• Designing balance loading architecture tailored to your target audience.
• Integrating Multicall3 for EVM networks and getTokenAccountsByOwner for Solana.
• Connecting fiat price feeds with caching.
• Developing token list UI with pull-to-refresh, search, and zero balance hiding.
• Testing on 10+ popular tokens in each network.
• Handing over access to App Store Connect / Google Play Console.
• Documentation for operation and one month of post-release support.

Estimated Timeline and Cost

Implementation typically takes 3 to 7 days depending on the number of networks and UI requirements. For a standard solution (EVM + Solana + prices) — 5 days. Estimated cost: $2,000–$5,000, varying with complexity. Contact us for a free project evaluation and precise timeline. Our engineers have 5+ years of mobile development experience and ensure compliance with App Store Review Guidelines and Play Console policies.

Order token balance display implementation for your wallet — get a turnkey solution. Get a consultation right now.

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.