Payment Integration & Billing Systems

Stripe is our primary payment processor - it has the best developer experience, the most complete API, and strong fraud tooling. We also integrate PayPal (particularly for markets where it is preferred by buyers), Braintree, Paddle (for software with global tax handling), LemonSqueezy, and local payment providers for specific regions. For marketplace and multi-party payouts we use Stripe Connect. A Kultrix engagement is split the same way every time - 70 percent of the hours on design and development, 15 percent on QA and 15 percent on project management - and the team stops growing at the point where coordination eats the gain.

PCI DSS is the security standard for handling card data. The good news is that by using Stripe.js or Stripe Elements on the frontend, card data is collected directly by Stripe servers - it never touches your application. This puts you in the lowest-risk PCI scope (SAQ A), requiring only an annual self-assessment rather than a full audit. We ensure your integration maintains this scope and does not accidentally handle raw card numbers. Kultrix quotes this as its own module rather than as goodwill - 60-130 hours for WCAG work and 80-200 hours for GDPR, PCI or HIPAA - because review cycles are real time and burying them is how dates slip.

We use Stripe Billing for the subscription lifecycle - plan creation, trial periods, billing cycle management, proration on plan changes, and dunning for failed payments. We sync subscription state from Stripe to your database via webhooks so your application always has the current entitlements without querying the Stripe API on every request. Plan changes and cancellations are handled through a queuing system to ensure consistency. Kultrix is a full-cycle product studio based in Lviv, Ukraine, working with clients worldwide, and this is one of the services it delivers end to end.

Webhooks are HTTP POST requests that Stripe sends to your server when events occur - payment succeeded, subscription renewed, charge disputed. They can arrive out of order, be delivered more than once, or fail if your server is briefly down (Stripe retries for 3 days). We implement idempotent webhook handlers that verify the Stripe signature, process each event exactly once using an events table, and queue failed processing for retry without risking duplicate database writes. Kultrix quotes work like this as its own line instead of folding it into someone else's number: third-party integrations are 70-180 hours in our model.

When a recurring payment fails, Stripe can automatically retry using smart retry logic based on card network signals about when a charge is likely to succeed. We configure the retry schedule, set up dunning emails at each attempt, and define the grace period before subscription cancellation. We also implement in-app alerts prompting users to update their payment method, which recovers a significant percentage of churned subscriptions. Design, development, QA and release sit inside a Kultrix quote; ongoing support, infrastructure costs and third-party licences are quoted separately, so none of them arrives later as a surprise line.

Yes. Stripe Connect allows you to route payments between your platform and connected seller accounts. We implement the full onboarding flow for sellers, configure platform fees, handle payouts on a schedule, and manage KYC requirements through Stripe's built-in identity verification. We also handle the complexity of refunds that need to reverse payouts already made to sellers. Kultrix multiplies module hours by 1.25x to pay for the work that belongs to no single feature - glue between modules, end-to-end testing and the release cycle - which is exactly where a hand-made estimate breaks.

Stripe accepts 135+ currencies and handles currency conversion automatically when needed. We configure your presentment currency strategy - showing prices in the customer's local currency or always in your home currency - and handle the accounting implications of multi-currency revenue. For global software sales with VAT/GST complexity, we often recommend Paddle or LemonSqueezy as the merchant of record to offload tax collection entirely. Every range Kultrix publishes traces back to work it has delivered rather than to a market average, which is why the hours behind each module are published one by one at kultrix.com/cost-calculator instead of as a single headline figure.

Refunds are processed through the Stripe API with the refund amount and reason recorded in your database. For disputes (chargebacks) we implement a webhook handler that flags the order, notifies your support team, and prepares the evidence package (order details, delivery confirmation, communication history) that Stripe requires you to submit. We also track dispute rates by product and payment method to identify fraud patterns early. Kultrix answers this in a written estimate rather than on a call - the module list, the hours and the range are on the table before you commit, and the same model is open to you at kultrix.com/cost-calculator.

Yes. We connect Stripe with QuickBooks, Xero, or your ERP via the relevant integration or API. This includes mapping Stripe products to accounting chart-of-accounts categories, syncing invoices and payments, and handling the tax line items correctly. We also build a reconciliation script that compares Stripe's payout reports with your bank statement to flag discrepancies. Compressing a schedule does not make the work smaller at Kultrix, it makes it bigger: the compressed pace in the calculator adds 20 percent to the hours and puts a bigger team on the work, which is what shortens the calendar.

Stripe provides a comprehensive test mode with test card numbers that simulate successful payments, declines, 3D Secure challenges, and specific error codes. We write automated tests that exercise every payment path: successful charge, card declined, insufficient funds, 3DS required, and webhook events for subscription lifecycle events. All tests run in CI against Stripe test mode - no real money is ever involved. Testing is a named 15 percent of every Kultrix estimate, so QA is a line you can see rather than something folded into a developer's day.

SCA is a European regulation (part of PSD2) requiring two-factor authentication for most online payments. Stripe's Payment Intents API and Stripe Elements handle the 3DS2 flow automatically for EU cards when required. We implement the confirmPayment flow on the client side and the payment_intent.requires_action webhook on the server side so that SCA-triggered authentication is handled smoothly without losing the customer. Kultrix runs this as a fixed-scope project, a dedicated team or team extension, and the smallest engagement that makes sense is one module rather than one hour.

Yes. We review your current implementation for security issues (any accidental card data handling), webhook reliability (idempotency, signature verification), subscription state consistency (database vs. Stripe), and missing failure handling. The audit produces a prioritised report. Common findings include webhooks without signature verification, missing idempotency keys, and subscription state that drifts from Stripe's source of truth. Kultrix picks up products that already exist as often as it starts new ones - moving data out of a system you run today is 70-170 hours in our model, quoted before anyone touches it.