Payment flows you can actually trust
We build the money layer of your product: multi-provider payment routing that fails over when one provider goes down, webhooks whose authenticity we cryptographically verify, and accounting math that stays exact to the last decimal. The result is a system where charges don't double-fire, currency totals reconcile, and you're not locked into a single processor.
The engineering, in plain terms.
Provider abstraction with fallback
We put every processor (bank rails and crypto gateways alike) behind one internal interface, so the app calls 'charge' once and we route to a healthy provider — automatically retrying through a backup when the primary errors or times out.
Cryptographically verified webhooks
Every incoming payment notification is checked against an HMAC/IPN signature before we trust a cent of it, with timing-safe comparison and replay protection so a forged or re-sent callback can never mark an order paid.
Idempotency against double-charges
Each payment attempt carries a unique idempotency key, so a retried request, a double-click, or a redelivered webhook settles exactly once instead of charging the customer twice.
Exact decimal money math
All amounts, multi-currency conversions, and commission splits use fixed-decimal arithmetic (up to 4 decimal places) instead of floating point — so live FX rates and partner payouts reconcile to the cent, every time.
From kickoff to launch.
- 1
Map the money flows
We document every state a payment passes through — initiated, pending, settled, failed, refunded — and define what each provider and webhook is allowed to change.
- 2
Build the provider layer
We implement the abstraction, fallback routing, and signed-webhook verification against each processor's real sandbox before any live key is touched.
- 3
Harden and reconcile
We add idempotency keys, replay protection, and decimal accounting, then test edge cases — timeouts, duplicate callbacks, partial failures — until totals always reconcile.
- 4
Go live with monitoring
We switch to production credentials behind feature flags, watch the first real transactions closely, and hand over a system you can audit.
Deliverables, and when it fits.
Deliverables
- A provider-agnostic payment integration with automatic fallback routing across multiple processors
- Signed-webhook handlers with HMAC/IPN verification, replay protection, and idempotent settlement
- Multi-currency accounting with exact decimal math and live FX-rate handling
- Optional KYC onboarding with passport/document OCR (MRZ extraction)
- A documented set of payment states, edge cases, and reconciliation rules
- Test coverage for the failure paths — timeouts, duplicate callbacks, double-submits
A good fit when
- You take payments through more than one provider and can't afford downtime when one fails
- You operate across currencies and need totals, conversions, and commissions to reconcile exactly
- You need verifiable webhook security and protection against double-charges
- You require KYC/identity onboarding with document capture as part of the flow
Shipped on a production multi-branch fintech CRM running three bank-rail providers with fallback routing, plus crypto payment integrations with IPN-verified webhooks and 4-decimal multi-currency commission math.
Want this for your product?
Tell us the goal — we scope it honestly.