Double-entry ledger, idempotency runtime, and settlement rail — with 416+ E2E tests included. Cloud-hosted from $99/mo, or own the source code for $299.
// Balanced ledger entry — 4 lines const entry = await this.ledger.postEntry({ debit: { accountId: 'user_alice', amount: 5000 }, credit: { accountId: 'revenue', amount: 5000 }, idempotencyKey: req.headers['x-idempotency-key'], }); // Idempotency — same key = same result // @Idempotent() handles it automatically @Post('/payments') @Idempotent() async createPayment(dto: CreatePaymentDto) { // Fires once. Even if called 10 times. return this.payments.process(dto); }
How it works
Create your account at dashboard.haylayn.com. Get your API key in 60 seconds.
Call the API. Money moves. Ledger records it. Idempotency handles retries automatically.
416+ E2E tests validate every module. Your team inherits production-grade infrastructure.
See it live
Watch the full stack come alive — auth, deposit, ledger verification, USDC settlement. Every command is real.
The problem
You have no idempotency layer. You refund manually and hope your support queue doesn't explode. It does.
Did the transaction record? Can you replay it? You don't know — because you built payments on top of a CRUD app.
You spend three days exporting CSVs, reconciling numbers that don't match, and questioning your life choices.
These aren't edge cases. They're Tuesday.
Meridian Core exists so you never build this infrastructure from scratch again.
Who built this
"I built HAYLAYN because every fintech startup in Latin America was solving the same infrastructure problems from scratch. Double-entry ledger, idempotency, settlement — these should be solved once, correctly, with tests. That's Meridian."
→ james@haylayn.comWhat's included
Each module solves a real problem that teams typically spend months building — and getting wrong.
Every peso has a source and a destination. Your books close correctly — always. Immutable, reversible, multi-asset, Decimal(36,18) precision.
The same webhook hits twice. You record it once. Full state machine — CREATED, PROCESSING, COMPLETED, FAILED, TIMEOUT. Exact response replay.
Events survive server restarts. FOR UPDATE SKIP LOCKED, exponential backoff with jitter, dead-letter support, HMAC-SHA256 signed payloads.
SHA-256 hash storage, timing-safe comparison, rotation, revocation, audit trail, admin and operator roles. No raw keys ever stored.
React UI with live health, outbox status, idempotency records, and SLA minute aggregates. No Datadog required for v1.
300 E2E contract tests included and passing across 30+ contract files. Validate every module before touching production. Docker Compose included.
Why HAYLAYN
Every fintech team eventually builds these. Most get them wrong the first time. Meridian ships them production-grade from day one.
Complete state machine (CREATED → PROCESSING → COMPLETED → FAILED → TIMEOUT). Every API call is safe to retry. No double charges, ever.
FOR UPDATE SKIP LOCKED, exponential backoff with jitter, dead-letter queue, HMAC-SHA256 webhook signatures. Your events are delivered exactly once.
Built-in settlement rail with Circle integration. Move USDC programmatically — wallets, transfers, and webhook verification included.
Every module ships with comprehensive end-to-end tests. Run them yourself. Production confidence from day one.
Build vs Buy
| Build yourself | With HAYLAYN ✓ | |
|---|---|---|
| Time to production | 6–12 months | ✓ 1 week |
| Team required | 2–3 senior devs | ✓ 1 dev |
| Double-entry ledger | Build from scratch | ✓ Included |
| Idempotency runtime | Build from scratch | ✓ Included |
| E2E test suite | Write yourself | ✓ 416+ included |
| USDC settlement | Integrate yourself | ✓ Circle ready |
| First production bug | Painful | ✓ Already fixed |
| Cost | $200k+ in salaries | ✓ From $299 |
What you can build
From wallets to BaaS — Meridian's primitives power the full spectrum of fintech products.
Multi-currency wallets with real-time balance tracking. Fund, transfer, and withdraw with full audit trail.
Process payments with idempotent retries and automatic reconciliation. Never lose a transaction in transit.
Credit lines, disbursements, and repayment tracking on a double-entry ledger. Every cent accounted for.
USDC settlement via Circle integration. Bridge fiat and crypto with a single API call.
Usage-based billing, credits, and invoicing. Track consumption per tenant with atomic counters.
White-label financial infrastructure for neobanks and fintechs. Multi-tenant from day one.
By the numbers
HAYLAYN Cloud
Full Meridian backend, managed by us. Your API keys, your dashboard, your data. Cancel anytime.
All plans include the full Meridian backend. Your code, your data. Cancel anytime.
Prefer to self-host? Own the source code →
Own the Source Code
No subscriptions. No vendor lock-in. Every module is standalone — buy only what you need. Private GitHub repo delivered instantly.
Everything you need to build a production payment backend with USDC settlement. Core included. Ship this week.
✔ 30-day money-back guarantee on all products. Email [email protected] if it doesn't fit your stack.
Built for modern payment rails
Before anyone can process a single USDC payment, they need a double-entry ledger, idempotent webhook processing, reliable event delivery, and API key governance.
That's exactly what Meridian Core provides — and Settlement Rail extends it with Circle USDC integration, smart routing, and compliance-ready audit trails.
Demo
Watch the full stack come alive — auth, deposit, ledger verification. Every command is real.
| ID | Type | Amount | Status | When |
|---|
| Endpoint | P50 | P95 | P99 | Success |
|---|---|---|---|---|
| POST /banking/deposit | 18ms | 42ms | 89ms | 100% |
| POST /fx/execute | 24ms | 56ms | 112ms | 100% |
| POST /auth/login | 31ms | 67ms | 134ms | 100% |
| POST /transfers/create | 22ms | 48ms | 95ms | 99.98% |
curl -X POST https://api.haylayn.com/payment-intents \ -H "X-Api-Key: hk_live_••••••••" \ -H "Idempotency-Key: $(uuidgen)" \ -d '{ "amount": 50000, "currency": "USD" }'
{ "id": "pi_abc123", "amount": 50000, "currency": "USD", "status": "CREATED", "idempotencyKey": "idem_xyz789", "ledgerEntries": 2, "balanced": true }
Start in Minutes
Your API key from the dashboard is all you need. No SDKs required — standard HTTP.
Request
# Create a payment intent curl -X POST https://api.haylayn.com/payment-intents \ -H "X-Api-Key: hk_live_your_api_key" \ -H "Content-Type: application/json" \ -H "Idempotency-Key: pay-$(uuidgen)" \ -d '{ "amount": 50000, "currency": "USD", "description": "Invoice #1234" }'
Response
{ "id": "pi_abc123", "amount": 50000, "currency": "USD", "status": "CREATED", "idempotencyKey": "idem_xyz789", "ledgerEntries": 2, "balanced": true }
Full API reference at api.haylayn.com/docs
Built for Production
No black boxes. Every claim is backed by code you can read.
All data encrypted with AES-256. API keys stored as SHA-256 hashes — no plaintext ever written to disk.
Comprehensive test suite included with every purchase. Run them yourself. Production confidence from day one.
Swagger documentation at api.haylayn.com/docs. Every endpoint documented. Full transparency.
Questions
Ready to build?
Create your account, get an API key, make your first call. Or buy the source code and self-host — your choice, your code.