Billing and payment solutions development

Billing and payment systems are the part of the business that has to be exactly right. A product feature that misbehaves annoys a user; a billing engine that misbehaves charges the wrong amount, misses a renewal or loses a settlement, and the cost lands directly on revenue and on trust. That is why we treat this work as infrastructure engineering, not feature work: every flow is designed to be auditable, every transaction traceable from authorisation to settlement.

This page covers the plumbing itself: the billing engine, the invoicing workflow, the acceptance layer and the reconciliation that ties them into one auditable record. The scope runs from back-office operations through to POS terminals, self-service kiosks and mobile apps, so a transaction behaves the same wherever it starts, whether the payment is a card tap, an invoice or a subscription renewal.

Few teams start from nothing - there is usually a provider checkout, a spreadsheet-driven invoicing process or a legacy billing system already in place, and the work starts from what exists rather than a blank page.

For the product layer above the payment plumbing - accounts, onboarding and the customer-facing build - see fintech solutions.

Every pricing decision your business makes eventually becomes a billing rule: the legacy plan a long-standing customer keeps, the discount sales agreed last quarter, the credit issued after a service incident. A billing engine is where that commercial policy is applied automatically, cycle after cycle, and it fails in two distinct ways. Policy that lives only in code is policy your finance team cannot audit; policy that lives only in spreadsheets is policy your operations team re-applies by hand every month.

• Proration when a plan changes mid-cycle, with credits applied the way finance expects
• Dunning sequences that decide when to retry, when to remind and when to suspend
• Grandfathered pricing that survives catalogue changes without manual exceptions every cycle
• Trial periods and promotions that end on the date the contract says

The deliverable is therefore not just working software but a written, tested rule set: each behaviour named, agreed with your finance team and pinned by automated tests, so when an auditor asks why an account was charged what it was, the answer is a document and a test rather than a search through code.

Payment acceptance is no longer one checkout page. A business that sells at the counter, online and in an app runs several acceptance surfaces at once - the capabilities grid on this page shows how many forms that takes. The engineering problem is not making each surface take a payment; any provider kit manages that. It is making every surface post into one shared transaction record, so a card tap at a POS terminal and a payment in the app produce entries finance can reconcile side by side.

Each new surface is a place where card handling, receipts and failure behaviour can diverge. We centralise acceptance logic behind one internal interface, so a refund behaves identically at a kiosk and in the app, and adding a channel is integration work, not a rebuild.

Mobile acceptance adds constraints the web never had: app-store review gates every release, and the platform vendor owns the secure hardware that payment code depends on. Desktop-era checkout flows never met either constraint. We design for the strictest surface first, so the same acceptance layer holds up wherever it is deployed.

When the acceptance layer itself has to ship inside other teams' apps, see embedding payments as an SDK.

Price follows scope, and in payments the scope drivers are concrete: how many acceptance surfaces you operate, how complex the billing model is, how many providers and back-office systems we integrate, and what certification the card schemes or your acquirer require. Discovery exists to fix those variables - it ends with a phased plan where each phase has a price and a deliverable you can hold us to.

The team is shaped to the work rather than sold as a fixed block: developers who have built payment flows before, UI/UX and testing where the product has a customer-facing surface, and management and analytics to keep scope, reporting and stakeholders honest. For ongoing billing operations a smaller retained team usually follows the build; for a bounded deliverable, the engagement can be a single sprint cycle.

That model is not hypothetical: when a missing payment SDK was blocking merchant onboarding at payabl., an EU-regulated merchant acquirer, the bounded engagement that closed the gap ran from kickoff to shipped software inside one sprint cycle.

Read the full case: the payment SDK shipped in a month.

The first month-end close is the real acceptance test of a payments build. Finance reconciles the period against what providers actually settled, and every transaction the system cannot explain becomes hours of manual chasing that erode confidence in the numbers. We scope detailed transaction analytics and reporting with the same weight as the payment flows themselves, so operations can read volumes, failures and settlement status directly instead of reconstructing them after the fact.

After launch we can run the system with you or hand it over entirely. Either way the operational scope is the same: monitoring and alerting on payment success rates, daily reconciliation against provider settlement files, dunning and reminder queues that are reviewed rather than fire-and-forget, and a change process for adding payment methods or invoice types without destabilising what already works.

Disputes and chargebacks are part of the same scope: when a cardholder challenges a transaction, the audit trail we built during development is what answers the case. The reporting layer keeps the evidence - authorisation, capture, settlement, refund - attached to every transaction, so responding is an export, not an investigation.