Off-Ramp: Selling Crypto for Fiat in Mobile Apps

Off-Ramp: Selling Crypto for Fiat in Mobile Apps

We've encountered this dozens of times: a client wants to withdraw cryptocurrency to a bank card, but the provider requires sending crypto first, with fiat arriving a couple of banking days later. Trust is the main barrier, solved by interface and transparency. In this article, we break down how we integrated off-ramp from Transak and MoonPay — turnkey, including KYC, SEPA, and push notifications. We assess your project — timelines from 5 to 12 days depending on complexity. Our experience: 5+ years in mobile fiat gateway development, 30+ integrations with payment providers. Over 5 years, we've launched 15+ off-ramp projects for fintech companies.

Why Off-Ramp Means Crypto Goes First

Unlike on-ramp, where the user first sees how much crypto they'll receive, off-ramp requires sending crypto to the provider's deposit address first. This creates an additional trust barrier. The interface must minimize anxiety.

Typical flow:

1. User enters the crypto amount and bank account details.
2. Provider issues a deposit address and confirms the rate (quote lifetime usually 15–30 minutes).
3. The app sends crypto to the deposit address — typically via the built-in wallet send screen.
4. Provider confirms receipt and initiates the fiat transfer.

KYC and Bank Account Verification

AML requirements for off-ramp are stricter. MoonPay and Transak require bank account verification via microtransactions (2 small debits for confirmation) or Open Banking (Plaid, TrueLayer).

The app must clearly inform the user about KYC timelines — verification can take 1–3 business days for the first off-ramp. Subsequent operations are instant after approval.

// iOS — launching Transak off-ramp widget
var components = URLComponents(string: "https://global.transak.com")!
components.queryItems = [
    .init(name: "apiKey", value: transakApiKey),
    .init(name: "walletAddress", value: userWalletAddress),
    .init(name: "defaultCryptoCurrency", value: "ETH"),
    .init(name: "productsAvailed", value: "SELL"), // only off-ramp
    .init(name: "redirectURL", value: "myapp://offramp-callback"),
    .init(name: "themeColor", value: "000000")
]
let safariVC = SFSafariViewController(url: components.url!)
present(safariVC, animated: true)

SEPA and Wire Transfer Support

For European users — SEPA Instant (credit within 10 seconds) and SEPA Credit Transfer (1–2 business days). For international — Wire (SWIFT, 2–5 days). Providers determine available methods based on user's country.

Transak supports SEPA for 30+ European countries. MoonPay supports SEPA, bank transfer for UK (Faster Payments).

Off-Ramp Provider Comparison

Why Off-Ramp Requires Triple-Check of Transactions

Due to the irreversibility of crypto transfers, each transaction is checked three times: locally in the app, on the provider side, and on the blockchain. We add a confirmation screen with details (address, amount, rate) and a timer. If the user doesn't confirm within one minute, the quote expires and the rate recalculates. This reduces error risk and builds trust.

How to Speed Up Withdrawals with SEPA Instant?

SEPA Instant is not available for all countries and banks. To use it, the provider must support this system and have a partner bank in the target zone. Transak covers 30+ countries through a partnership with a UK bank. We recommend using SEPA Instant as the primary method for Europe — 10 seconds vs 1–2 days for standard SEPA. The interface should highlight this option as recommended.

Status and Notifications

An off-ramp transaction goes through several statuses: crypto_received → processing → fiat_sent → completed. Each transition triggers a push notification. The user should never guess the stage.

// Android — webhook status handler (server-side, pushed to device)
when (webhookEvent.status) {
    "AWAITING_PAYMENT_FROM_USER" -> sendPush("Awaiting your transfer of $amount $currency")
    "PAYMENT_DONE_MARKED_BY_USER" -> sendPush("Crypto received, verification in progress")
    "ON_HOLD_PENDING_DELIVERY_FROM_TRANSAK" -> sendPush("Transfer initiated")
    "COMPLETED" -> sendPush("$fiatAmount ${fiatCurrency} sent to your account")
    "FAILED" -> sendPush("Transaction declined: $reason")
}

What's Included (Deliverables)

• Integration of one off-ramp provider (Transak or MoonPay) — 5 days.
• Multi-provider configuration with switching — 8–12 days.
• Includes: amount input UI, redirect handling via deep links, status retrieval via webhooks, push notification setup.
• Documentation of the flow and architecture.
• Support during App Store / Google Play release.

Timeline: 5 days for a single provider, 8–12 for multi-provider. Contact us to assess your project — receive a consultation on provider choice and architecture. We guarantee transparency and compliance with SEPA and App Store Review Guidelines (section 5.1).

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.