EIP-1559 in Mobile Wallet: Type-2 Transactions

A user sends ETH, and the transaction gets stuck for hours or a huge fee is deducted. Before EIP-1559, wallets guessed gasPrice and often got it wrong. We, as a team with 5 years of experience in mobile wallet development, implement this standard to eliminate overpayments and delays. EIP-1559 makes fees predictable: the user sets a maximum gas price (maxFeePerGas) and a validator tip (maxPriorityFeePerGas), while the protocol automatically calculates the base fee (baseFee), which is burned. The result is savings of up to $0.50 per transaction compared to the old format and no stuck transactions. Official specification: EIP-1559. Today, EIP-1559 support is standard for modern wallets — without it, users switch to competitors. Our solution ensures smooth integration with minimal modifications.

How Type-2 Transactions Work in a Mobile Wallet

A type 2 transaction contains three key parameters instead of a single gasPrice:

• baseFee — automatically calculated by the protocol, burned (does not go to the miner). Increases by 12.5% when the block is full, decreases when empty. Get the current value: eth_getBlockByNumber("pending", false) → field baseFeePerGas.
• maxPriorityFeePerGas (tip) — reward for the miner/validator. Minimum tip for block inclusion is usually 0.1–2 Gwei.
• maxFeePerGas — absolute maximum the user is willing to pay. Actually deducted: min(maxFeePerGas, baseFee + maxPriorityFeePerGas). The difference is refunded.

// iOS — web3swift: building an EIP-1559 transaction
var transaction = CodableTransaction(
    type: .eip1559,
    to: recipientAddress,
    value: amount,
    data: Data()
)
transaction.maxFeePerGas = baseFee + maxPriorityFee + buffer
transaction.maxPriorityFeePerGas = maxPriorityFee
transaction.chainID = BigUInt(1) // Ethereum Mainnet

How to Properly Display Fees to the User

The user sees maxFeePerGas = 50 Gwei, but if baseFee at the time of mining is 20 Gwei and tip is 2 Gwei, they will pay 22 Gwei. The remaining 28 Gwei are refunded. In the UI, it is better to display the expected fee (baseFee + tip) and the maximum possible fee (maxFeePerGas * gasLimit). This reduces anxiety for users who see a large maximum. Fee cost reduction reaches 30-50%.

Dynamic Fee Suggestions: How to Configure?

Recommended values should be updated every 12 seconds (Ethereum block time). Sources:

• eth_feeHistory — calculate percentile priority fee yourself
• eth_maxPriorityFeePerGas — MetaMask method, supported by Infura, Alchemy, QuickNode
• Blocknative Gas API — paid but very accurate for Mainnet

// Android — get recommended priority fee
val maxPriorityFeeResponse = web3j.send(
    Request("eth_maxPriorityFeePerGas", emptyList<Any>(), web3jService, EthMaxPriorityFeePerGas::class.java)
)
val priorityFeeWei = maxPriorityFeeResponse.maxPriorityFeePerGas

Comparison of Legacy and EIP-1559 Transactions

EIP-1559 transactions are 25% cheaper than legacy gas auctions and 2x faster for urgent transactions.

Comparison of Dynamic Fee Sources

How to Handle Networks Without EIP-1559 Support?

BNB Chain uses legacy format with a fixed gasPrice (default 3 Gwei). Polygon supports EIP-1559 from network version 26.x. Arbitrum and Optimism have their own mechanisms on top of EIP-1559. The app must detect the network type and automatically choose the appropriate transaction format. Sending a type-2 transaction to a network without EIP-1559 will return an error unsupported transaction type. When receiving such an error, the app should switch to legacy format: replace type: .eip1559 with type: .legacy and specify gasPrice instead of maxFeePerGas and maxPriorityFeePerGas. It is recommended to cache the network type after the first successful send.

Benefits of EIP-1559 Integration

Legacy wallets with a single gasPrice force users to overpay or wait hours for confirmation. Implementing EIP-1559 provides predictability, savings of up to $0.50 per transaction, and user trust. Most modern wallets (MetaMask, Trust Wallet) already support EIP-1559 — your wallet should not fall behind. Get a consultation on integrating EIP-1559 into your project.

What's Included in the Implementation

• Audit of the current wallet and identification of necessary changes.
• Implementation of type-2 transactions with correct parameter calculation.
• Integration of dynamic suggestions via RPC methods.
• UI/UX: display of expected and maximum fees, auto-update.
• Support for multiple EVM networks with auto-detection and fallback.
• Testing on mainnet and testnet with extreme scenarios.
• Documentation, repository access, team training, and post-implementation support.

We guarantee correct operation across all popular networks, leveraging proven methods and experience from over 50 implemented projects. Request an audit of your current wallet — we will prepare a transition plan to EIP-1559.

Timeline: 2–3 days for basic integration, from 5 days for complex projects with multiple networks. The cost is determined after an audit. Contact us for a consultation and project evaluation.

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.