How to Build a Fintech App: Payments, Wallets, Onboarding and Compliance

What is a fintech app, and what does it take to build one?

A fintech app is a mobile or web application that lets a user hold, move, borrow or manage money, with a licensed bank, payment processor or scheme doing the regulated work behind the screen. The app is the surface; the money moves on rails owned by somebody else. Every decision about how to build a fintech app follows from which rails you use and who holds the license.

The World Bank Global Findex 2025 reports that 79% of adults worldwide have an account, 1.3 billion still do not, and 42% of adults in low- and middle-income economies made a digital merchant payment in 2024, up from 35% in 2021. A Bank for International Settlements working paper tracking 86,163 finance apps across 95 countries found that adoption rises after a country launches a fast payment system, most in lower-income economies. The rails come first; the apps follow.

• Know Your Customer (KYC) onboarding is a regulated identity check, and the Financial Action Task Force (FATF) accepts reliable digital identity for remote onboarding under a risk-based approach.
• A payment gateway integration that tokenizes card data at the processor keeps most of PCI DSS out of scope; handling raw card numbers can mean more than 300 controls.
• A digital wallet that holds customer balances needs a double-entry ledger and, in most jurisdictions, an e-money or money transmitter license or a licensed partner.
• Sigi Technologies has shipped payments-integrated platforms on Stripe, Stripe Connect, Paystack and PayPal, and has not shipped a bank or neobank.

What has to be right before you design a single screen?

Most fintech app development projects stall on four questions nobody wrote down. Answer them in discovery, in this order.

• Where the money sits. Pass-through means the processor pays the merchant and you never hold a balance. Stored value means you owe the customer a balance: a wallet, and a regulated liability.
• Who verifies identity. Either the processor verifies the account holder, or you run KYC onboarding through an identity vendor and own the outcome. Mixing the two without a written rule is how gaps appear.
• How much card data touches your systems. Hosted fields plus a stored token shrink your PCI DSS scope to the shortest self-assessment questionnaire.
• Which license covers the activity. Card acceptance, payouts, holding balances, lending and cross-border transfers each need a permission, yours or a partner’s, before launch.

What features should a fintech app have?

Fintech app features split by journey rather than by screen. This is what a payments product needs at launch.

Onboarding, payments, cards, buy now pay later and cross-border

• Identity proofing at sign-up with ID capture, a liveness selfie and sanctions screening, then strong customer authentication for login and payment confirmation: a device you hold plus a biometric or PIN.
• Add a card or bank account through the processor’s tokenized form, never your own input fields, and pay or top up against a server-side quote shown before confirmation.
• Card issuing through a processor or bank partner, with freeze, limits and merchant category controls in the app.
• Buy now pay later as an installment schedule attached to a purchase, with the lender of record named.
• Cross-border payments with the exchange rate, fees and arrival estimate shown up front, because the quote is the product.

Operations and admin

• A back office that sees every customer, transaction and payout, with role-based access enforced at the API.
• Daily reconciliation between the ledger, the processor settlement report and the bank statement.
• Alert queues for failed KYC checks, chargebacks and stuck payouts, plus an audit trail of every limit, fee or status change.

How does KYC onboarding work in a fintech app?

KYC onboarding is the process of collecting a new customer’s identity details, verifying them against an independent source, and screening the person before the account can transact. The FATF Guidance on Digital Identity sets the baseline: firms may rely on digital identity for customer due diligence under a risk-based approach, and remote onboarding on a reliable, independent digital ID with safeguards can present a standard or even lower level of risk. National regulators such as the UK Financial Conduct Authority and the Saudi Central Bank set the document and threshold rules.

The product decision is how much to ask for, and when. Stripe’s Connect identity verification documentation describes up-front onboarding, which collects everything at sign-up, and incremental onboarding, which asks for more as volume grows, and warns platforms not to rely on its verification for an independent legal KYC obligation. Processors verify the account they pay out to; you own the rules that apply to your product.

How do you integrate a payment gateway into a fintech app?

Payment gateway integration is the connection between your app and the processor that authorizes, captures and settles a payment. Tokenization decides the design: the customer types card details into a field the processor controls, the processor returns a token, and your servers only ever see the token. Stripe’s integration security guide states that a business handling raw card data may need to meet more than 300 PCI DSS controls, while its hosted and mobile integrations send card data straight to Stripe. Adyen and Checkout.com work the same way.

Three decisions follow. First, every payment state comes from the processor’s webhooks, with signatures verified so a forged event cannot mark an order paid. Second, strong customer authentication must be designed in for European customers. The EU regulatory technical standards on strong customer authentication require two or more elements from knowledge, possession and inherence, with exemptions for remote transactions under EUR 30 and for low-risk transactions under transaction risk analysis. In practice that means 3D Secure 2, which Adyen’s documentation describes as frictionless when the issuer is satisfied by device data and a challenge when it is not, with liability shifting to the issuer. Third, the quote shown and the amount captured must come from one server-side calculation.

If the app pays out to sellers, drivers or partners, the gateway question becomes a marketplace question. Stripe Connect lets a platform collect a payment and automatically pay a portion to the seller or provider, with verification and payouts handled per connected account. Sigi used it on Busy Bean Coffee and ServiPR; the mechanics are covered in the companion guide to Stripe Connect marketplace payouts.

How do you build a digital wallet inside a fintech app?

A digital wallet is a stored balance a customer can fund, spend and withdraw, held by the operator on the customer’s behalf. Digital wallet app development therefore starts with the ledger, not the screen. Every top-up, payment, refund and fee is a double-entry posting, the visible balance is the sum of those postings, and all customer balances together must equal the money held at the bank or processor.

The second decision is the funding rail. Cards are universal and expensive; bank transfers are cheaper and, with open banking, can be initiated from inside the app. In the United Kingdom, Open Banking Limited reported 15.16 million users in July 2025, close to one in three adults. The Saudi Central Bank issued its Open Banking Framework in November 2022, account information first and payment initiation second. For a wallet, payment initiation means a top-up that costs a fraction of a card fee and settles in near real time.

On proof, plainly: Sigi has not shipped a stored-value wallet or a bank. Its delivered pattern keeps funds at the processor, as on ServiPR, or runs a ledger of order-stage entries over the processor, as on Busy Bean. On Pacifrica Express, a cross-border logistics platform, payment is taken by card, Paystack or PayPal only after the warehouse validates the order, with email one-time password verification to keep throwaway registrations out of a payment-bearing flow.

What does PCI DSS compliance for apps actually require?

The Payment Card Industry Data Security Standard (PCI DSS) is the card schemes’ security standard for any entity that stores, processes or transmits cardholder data. The PCI Security Standards Council retired version 3.2.1 on 31 March 2024, so version 4.0 and its 4.0.1 update are the only standard in force. An app that never touches a raw card number validates through Self-Assessment Questionnaire A (SAQ A), the shortest form. In January 2025 the Council removed requirements 6.4.3, 11.6.1 and 12.3.1 from SAQ A in favor of an eligibility criterion: the merchant must confirm its site is not susceptible to script attacks on its e-commerce systems, effective 31 March 2025.

For a product owner that is four requirements: collect card data only through the processor’s hosted fields or mobile SDK, serve payment pages over TLS 1.2 or later with third-party scripts kept off them, store only the token, card brand, last four digits and expiry, and attest annually. Sigi is a software firm, not a PCI-certified service provider. On Busy Bean, card data is tokenized by Stripe and never touches the client’s servers; that is the pattern Sigi builds to, not a certification it holds.

Do you need a license to build a fintech app?

It depends on what the app does with the money. Accepting card payments for your own goods needs a merchant account, not a license. Paying out to third parties, holding balances, lending or cross-border transfers each need a permission: an electronic money or payment institution authorization in the UK and EU, state money transmitter licenses in the United States, a Saudi Central Bank license or sandbox place in Saudi Arabia. Most early-stage fintech apps launch under a licensed partner’s permissions and apply for their own once volume justifies it. Name both in discovery, before any estimate is signed.

How much does it cost to build a fintech app?

Fintech app development cost follows the same drivers as any multi-surface product: how many user types, one codebase or two, and how much admin and reconciliation must be production-grade on day one. Sigi attaches no figure to any named build. The ranges below are typical-scope planning estimates, consistent with Sigi’s guide to how much it costs to build a mobile app. Licensing, legal and audit fees sit outside them.

A stored-value wallet, card issuing or lending pushes a build past the top tier, because the ledger, the compliance program and the partner integration each add scope. Guides ranking for this query commonly cite five to eleven months for a first release; treat that as a market figure. Sigi quotes from a written brief.

Should you build on a processor, a banking-as-a-service provider, or your own ledger?

Build on a payment processor when the product is pass-through: customers pay, providers get paid, nobody holds a balance. Stripe, Adyen and Checkout.com carry card acceptance, tokenization, 3D Secure and, through connected accounts, payouts. It is the fastest route to market and the one Sigi has shipped repeatedly. Build on a banking-as-a-service provider when the product needs accounts, stored balances or cards and you hold no license; the provider supplies license, ledger and card program, and pricing, limits and roadmap belong to the partner.

Build your own ledger when the money model is the business: splits, holds, installment schedules or multi-currency balances no partner models cleanly. Busy Bean needed this for commission rules and check-clearing holds, so its ledger is custom while card processing stays with Stripe. A custom ledger on a partner’s rails is the usual honest answer; a custom ledger on your own rails is a bank.

How to build a fintech app step by step

The sequence Sigi follows for a payments-integrated product; each step fixes a decision the next depends on.

1. Write the money model: every event that moves value, who owes whom afterwards, and whether any balance is held. This decides the license question and the ledger design.
2. Name the regulator and the licensed partner, and confirm which obligations, such as KYC record-keeping, remain yours.
3. Design the onboarding journey by risk tier: what is collected at sign-up, what at a volume threshold, and what happens to a customer under review.
4. Choose the processor and the integration pattern: hosted fields or mobile SDK for card capture, connected accounts if there are payouts, webhooks as the source of truth.
5. Model the ledger before the screens: accounts, postings and daily reconciliation against the settlement report and bank statement.
6. Design the customer app, then the provider app, then an internal admin that is correct rather than beautiful.
7. Test the unhappy paths in automated suites on every pull request, as on Busy Bean: failed 3D Secure challenges, duplicate webhooks, refunds after payout, a bounced check, an expired verification.
8. Complete the PCI DSS self-assessment, run a penetration test on the payment surfaces, submit to the stores and switch on alert monitoring before the first real customer.

Related reading

For the three-sided pattern behind most payout products, read the guide to building a multi-vendor marketplace and the companion piece on Stripe Connect marketplace payouts. The cost bands above come from how much it costs to build a mobile app. If the product needs an in-app support assistant, see the guide to building an AI chatbot. For the shipped proof, see the Busy Bean Coffee case study and the ServiPR services marketplace case study. If you are scoping a payments-integrated product, see Sigi’s fintech software development practice or send a brief.