A checkout that passes in a test environment can still fail on a busy Thursday. The issuer asks the shopper for authentication, the bank rejects a charge that looked fine, the same webhook arrives twice, and finance finds an order marked paid that was never captured. Most of the work in payment integration sits in the cases around the happy path.
We connect Stripe, PayPal, Square, and Revolut accounts to web and mobile products, add Apple Pay and Google Pay where the device and the gateway allow it, and keep the surrounding machinery consistent: refunds, disputes, subscriptions, invoices, and payouts to sellers. Which gateway you choose matters less than how the money movement is recorded in your own database.
What the integration covers
Checkout architecture
There are three practical shapes. A hosted checkout page (Stripe Checkout, PayPal Smart Buttons) launches fastest and keeps the smallest compliance footprint. Embedded fields inside your own page give you control over layout while card data still goes straight to the gateway. A server-side integration gives the most control and the largest compliance burden.
Bank transfer flows belong here too: SEPA and local transfer instructions, a payment reference per order, matching of incoming transfers to invoices, and a screen for cases where someone confirms receipt before goods ship.
Cards, wallets, and local methods
Card payments through your chosen gateway, plus wallets: Apple Pay with the domain verification file and merchant identifier in place, Google Pay through the gateway's wallet integration, and tokenised cards so returning buyers do not re-enter details. Multi-currency pricing and settlement currencies get configured explicitly, because a store that displays euros and settles in pounds creates accounting problems later.
SCA and 3D Secure
Strong Customer Authentication rules in the UK and the EEA affect every card payment to a European issuer. We implement the 3D Secure 2 challenge flow, request frictionless exemptions where the rules permit, and label merchant-initiated transactions correctly so subscription renewals are not treated as new customer payments. A soft decline triggers a retry path and a message that explains what the customer should do next.
Subscriptions and invoices
Recurring billing with Stripe Billing or PayPal subscriptions: plans, trials, upgrades with proration, dunning emails for failed renewals, and the webhook handling that locks access when a payment finally fails. We generate invoices with the tax fields your accountant needs, and we keep the subscription state in your database rather than reading it from the gateway on every page load.
Refunds, disputes, and reconciliation
Refunds are idempotent and partial refunds are supported, with each one written back to its order. Disputes come with short evidence deadlines, so dispute webhooks route to a queue your team can act on, with the original order, delivery proof, and customer communication in one place. A nightly reconciliation job compares gateway balances, fees, and settlements against your internal ledger and reports the differences.
Payouts for marketplaces
Split payments for platforms use Stripe Connect or an equivalent: seller onboarding with identity checks, separate charges and transfers, application fees, payout schedules, and handling for negative balances and reserves. This is the part of payment work with the most rules to get right, and it fits with our marketplace platform development projects.
Webhooks that survive contact with production
Signature verification on every inbound event, the raw request body preserved for validation, and processing keyed by the gateway event id so a duplicate delivery cannot create a duplicate order. Events go into a queue, failures retry, and anything that still fails lands in a dead-letter table with an alert. We design these endpoints as part of our API development and integration work.
PCI scope and what we avoid storing
We keep card numbers, security codes, and full track data out of your systems entirely. Card fields come from the gateway, tokens replace stored instruments, and we check that no card data leaks into application logs, error trackers, or admin screens. That keeps most merchants on a short self-assessment questionnaire.
Who this is for
- Online stores taking card, wallet, and bank transfer payments in more than one currency
- SaaS and membership products billing on a monthly or annual cycle
- Marketplaces and platforms that collect money from buyers and pay sellers
- Service businesses taking deposits against a quote
- Fintech teams that need a payment layer behind their own branded interface
What we deliver
A working checkout and the records behind it
The customer-facing flow, and the internal side that finance depends on: order records, payment states, fee and settlement entries, and a reconciliation report that can be run on demand.
Gateway accounts set up properly
Business account configuration, products and prices, webhook endpoints, wallet domain verification, tax settings, and the sandbox credentials your developers need, all documented rather than left in a chat thread.
Test coverage for the awkward cases
Expired cards, insufficient funds, authentication failures, duplicate submissions, refunds after partial fulfilment, and disputed charges, each reproduced in sandbox.
A cutover and handover plan
A tested switch from test keys to live keys, a small live transaction check, monitoring on failed payments, and runbooks for refunds, disputes, and payout issues.
How the engagement runs
Week one is discovery: your business model, your gateway accounts and their verification status, currencies, tax rules, and whether money is split between parties. This phase decides the checkout architecture and produces a short written scope.
The build happens in sandbox next, typically over two to four weeks for a single gateway store with cards, wallets, and one recurring product. We build the checkout, wire the webhooks, and add the admin views your team needs. Marketplace payouts with seller onboarding take longer, usually six to ten weeks, because identity verification and payout rules need testing with real vendor conditions.
Before launch we run the failure cases, check reconciliation against sandbox settlement data, and review PCI scope with you.
What it costs
Work is billed at our flat rate of $39 per hour, or as a fixed scope once discovery is complete. Both models, and the monthly capacity option, are described on the pricing page.
Scope usually moves with four things: how many gateways and payment methods you need, whether billing is one-off or recurring, whether funds are split between sellers, and how much of the existing order data has to be migrated. A single-currency store with cards and wallets is a short phase. A platform paying sellers in several currencies needs its own compliance review.
Proof
Paymentz is a fintech platform for international transactions, mass pay-ins and pay-outs, and local IBAN support, built with a white-label option for client branding. It shows that we can model high-volume money movement underneath a product that other companies put their own name on.
Paykolo covered online banking workflows for businesses and individuals, including pay-ins, pay-outs, and local IBAN handling on a Laravel, Ruby and React stack. It is our evidence that transaction state, security boundaries, and operational screens can ship together in one accountable delivery.
Simetria needed a business audience to understand cross-border collections through local IBANs and consolidated cash flow. Payment products often lose buyers at the explanation stage, and this work shows how we present payment mechanics in plain commercial language.
Erabanq is an account-to-account payment platform built around lower transaction costs than card schemes. It demonstrates that we can build payment flows outside the card networks, where bank transfers and references replace authorisation and capture.
Related services
- Web development for the application work around the payment layer
- Fintech and Web3 development for regulated financial products, wallets, and on-chain payments
- E-commerce store development when you need the shop built along with the checkout
- Marketplace platform development for multi-vendor flows and seller payouts
- Mobile payment and wallet integration for Apple Pay, Google Pay, and wallets inside mobile apps
Next step
Send us the gateway you use, or the one you are considering, and describe how money moves through your business: who pays, who receives, and in which currencies. We will tell you what the integration involves and which parts carry compliance risk.
Contact us with your current checkout details, or run your requirements through the Vasilkoff.info estimator for an initial scope and cost range.