StablePeg
Achala Arunalu Achala Arunalu Fintech Stablecoin IC Stablecoin banking | Cards | Crypto payments | Fraud/AML | Treasury ops LinkedIn

Interactive API walkthrough

Learn the merchant edge and treasury engine as one connected system.

Use this guide as a product map, not a pile of API pages. Start with the recommended path, use the master map when you need the whole system, and use the canonical topic map to avoid repeating the same KYC, KYT, provider, ledger, and webhook ideas in every section.

Find my path View library Open master map Find topic owner
Merchant Checkout app
External edge Crypto Payments API
Risk + treasury Treasury Settlement API
Quote, intent, risk decision, card authorization, dispute control, sandbox simulation, provider adapter, secured event, ledger conversion, payout, playbook.
Achala Arunalu

Built by Achala Arunalu

Fintech stablecoin IC for product teams building real money systems.

I build practical product architecture across stablecoin banking, card issuing, crypto payments, fiat rails, fraud and AML, treasury settlement, reconciliation, and internal operations tooling.

Stablecoin banking Cards + recon Crypto payments KYC/KYT/AML Treasury ops
Connect on LinkedIn Explore the field guide

Guided path finder

Start with the fintech job you are doing

Pick a product persona and the problems you need to solve. The site will trim the tutorial library to the most useful path so you are not forced through every section.

1. Choose your lens

2. Add current needs

Master platform map

How products, providers, custody, and the customer ledger connect

Each product has its own lifecycle, but all money-impacting paths meet at the same control points: risk and identity decisions, provider adapters, custody infrastructure, and the internal customer ledger.

Product surfaces

Crypto Payments API Quotes, payment intents, deposits, settlement, refunds.
Stablecoin Cards API Cardholders, cards, controls, authorizations, holds.
Card Ops + Ops Controls Clearing, disputes, exceptions, customer-safe status.

Decision layer

Fraud, AML, and KYT Sardine-style fraud signals, wallet risk, transaction monitoring, cases.
KYC / KYB eligibility Sumsub-style applicants, review results, card and payout eligibility.
Security + events Scopes, idempotency, signatures, audit, event catalog, replay.

Provider adapters

Rain card issuing Provider cards, auth callbacks, clearing files, dispute events.
Fireblocks or BitGo custody Vaults, deposit addresses, wallet policy, on-chain transactions.
Fiat & local rails Noah, Tazapay, Infinia-style integrators, banks, PIX, SPEI, ACH, SEPA.

Financial truth

CustomerLedgerAccount Available balance, holds, posted debits and credits, fees, adjustments.
Ledger entries Deposit credit, card hold, card debit, refund debit, payout debit.
Recon and finance Provider records, custody balances, settlement batches, reports.

Fireblocks or BitGo is the custody infrastructure that observes and moves on-chain assets. The internal customer ledger is the balance source of truth: deposits credit it, card authorizations reserve it, clearing posts debits, refunds and payouts reduce it, fiat rails move local money, and reconciliation proves it.

Canonical topic map

Where each idea should live

If a section only touches a topic, link to the owner below instead of restating it. This keeps the tutorial focused and makes future changes easier.

Merchant checkout Crypto Payments

Quote, intent, deposit detection, merchant settlement, refund initiation.

 Fraud, AML, KYT Fraud & AML

Risk decisions, wallet exposure, sanctions, transaction monitoring, cases.

 Identity proof KYC / KYB

Applicants, provider review, eligibility, resubmission, ongoing monitoring.

 Card issuing Stablecoin Cards

Cardholders, card provisioning, controls, first authorization decision.

 Card transaction ops Card Ops

Authorization holds, clearing, settlement, auto-recon, manual recon.

 Exceptions Ops Controls

Disputes, freezes, holds, releases, evidence, customer-safe status.

 External providers Provider Adapters

Sardine, Sumsub, Rain, Fireblocks, BitGo, bank rails behind contracts.

 Local money Fiat & Local Rails

Noah, Tazapay, Infinia-style providers, local banks, PIX, SPEI, ACH, SEPA.

 Security API Security

Scopes, idempotency, signatures, approvals, audit, key rotation.

 Async contracts Event Catalog

Event types, schemas, delivery, retries, replay, ownership.

 Object truth Data Model

CustomerLedgerAccount, custody wallets, ledger entries, lineage, recon links.

 Money execution Treasury

Custody, ledger posting, minting, burning, staking policy, FX, payout rails.

 Operating model Playbooks

Case triage, incidents, escalation, glossary, metrics, postmortems.

Tutorial library

Fifteen focused sections

Open a section when you need the detail. Each page now declares what it owns and links out for related topics.

Showing the recommended path for Stablecoin banking PM.

Merchant-facing 6 lessons

Crypto Payments API

Learn how merchants lock a price, create a payment intent, wait for chain confirmations, settle funds, and issue refunds as new transfers.

  • Quote expiry and consumed quotes
  • Payment intent lifecycle
  • Signed webhooks and retry safety
Open tutorial
Risk controls 5 lessons

Fraud & AML Engine

Learn how product events flow into a fraud engine, how decisions come back, and where a Sardine-like provider fits for fraud, AML, device, and case signals.

  • Allow, step-up, review, and block decisions
  • AML screening and ongoing monitoring
  • Provider adapter and webhook pattern
Open tutorial
Identity 6 lessons

KYC / KYB with Sumsub

Learn how applicants are created, how verification is handed off to a Sumsub-style provider, and how review results gate stablecoin cards.

  • Applicant and verification level setup
  • Document, liveness, sanctions, and review result flow
  • Eligibility signal for card provisioning
Open tutorial
Issuing 6 lessons

Stablecoin Cards

Learn how KYC-approved cardholders are provisioned, how Rain-style card issuing connects behind an adapter, and how a real-time card authorization is approved or declined.

  • Cardholder, card, and controls setup
  • Fast authorization decision endpoint
  • Holds, clearing, and future reconciliation hooks
Open tutorial
Card operations 8 lessons

Card Auth, Clearing & Recon

Learn the operational lifecycle after a card exists: real-time authorization, reversals, clearing, issuer settlement, auto-recon, and manual reconciliation.

  • Authorization decisions and hold expiry
  • Clearing, settlement, and ledger posting
  • Auto-recon and exception workflows
Open tutorial
Ops controls 6 lessons

Disputes & Ops Controls

Learn how refunds, card disputes, chargebacks, freezes, AML holds, evidence packs, and operational SLAs work across crypto and card products.

  • Crypto exceptions and refund decisions
  • Card dispute evidence and outcomes
  • Risk holds, freezes, and release controls
Open tutorial
Sandbox 6 lessons

Testing, Sandbox & Webhooks

Learn how to simulate crypto payments, card authorizations, provider webhooks, retries, failures, idempotency, and go-live readiness.

  • Deterministic sandbox fixtures
  • Signed webhook delivery, retry, and replay
  • Scenario clocks, failures, and edge cases
Open tutorial
Money journey 7 lessons

End-to-End Money Journey

Follow value from checkout through risk, custody, ledger, settlement, card spend, clearing, reconciliation, disputes, and finance reporting.

  • One map across crypto, cards, and treasury
  • Ledger, holds, settlement, and recon truth
  • Events that tell every service what changed
Open tutorial
Architecture 6 lessons

Provider Adapter Architecture

Learn how Sardine, Sumsub, Rain, Fireblocks, BitGo, fiat rail providers, banks, and country integrators sit behind stable contracts and mappers.

  • Stable internal contracts over provider payloads
  • Command, webhook, mapper, and outbox pattern
  • Versioning, idempotency, and provider health
Open tutorial
Local rails 6 lessons

Fiat & Local Rails

Learn how local fiat collections and payouts route through country rails like PIX, SPEI, ACH, SEPA, and Faster Payments without mixing rail state with customer ledger truth.

  • Rail vs currency, cutoffs, and country requirements
  • Noah, Tazapay, Infinia-style adapters and local banks
  • Ledger impact, provider obligations, and fiat reconciliation
Open tutorial
Operations 8 lessons

Ops Playbooks & Glossary

Give support, risk, finance, product, and engineering a shared operating language for incidents, cases, SLAs, glossary terms, and escalations.

  • Playbooks for common payment breaks
  • Risk, AML, dispute, and settlement escalation paths
  • Glossary that makes terms unambiguous
Open tutorial
Security 6 lessons

API Security & Auth

Learn API keys, service tokens, scopes, idempotency, webhook signatures, audit logs, key rotation, and privileged operations control.

  • Scoped auth and least privilege
  • Idempotency, audit trails, and approvals
  • Signed webhooks and replay protection
Open tutorial
Events 7 lessons

Event Catalog

Build the canonical event list for payment, risk, identity, card, ledger, provider, ops, and finance updates.

  • Producers, consumers, retries, and replay
  • Event families across every product layer
  • Schemas, versions, and operational ownership
Open tutorial
Data model 7 lessons

Canonical Data Model

See how merchants, applicants, cardholders, wallets, custody accounts, customer ledger accounts, transactions, and cases relate.

  • Object relationships and ownership boundaries
  • Fireblocks or BitGo custody to customer ledger
  • Ledger-affecting objects and reconciliation links
Open tutorial
Internal service 8 lessons

Stablecoin Settlement & Treasury API

Follow the system beneath the merchant API: Fireblocks custody, USDC ledgering, mint and burn lifecycle, optional staking policy, locked FX quotes, and dual payout rails.

  • Deposit addresses and custody
  • Double-entry USDC ledger
  • Mint, burn, stake, payout, and reconcile
Open tutorial

Mental model

How the APIs compose

Use this table when deciding where a concept belongs. The first column is the owner; other pages should link back instead of repeating the same explanation.

Layer
Primary job
Objects to watch
Crypto Payments API
Accept crypto payments and settle merchant funds without requiring early customer KYC in the checkout flow.
PaymentQuote, PaymentIntent, Settlement, Refund, paymentEvent.
Fraud & AML Engine
Normalize risk events, run KYT transaction monitoring, call Sardine-like providers, and return decisions to product and treasury services.
RiskSession, RiskEvent, RiskDecision, KytTransaction, AmlScreening, Case, providerWebhook.
KYC / KYB
Verify people and businesses, map provider review results, and publish eligibility for regulated products.
Applicant, VerificationLevel, AccessToken, ReviewResult, EligibilityDecision, sumsubWebhook.
Stablecoin Cards
Provision KYC-approved cardholders and authorize card spend against stablecoin balances through a Rain-style issuer adapter.
Cardholder, Card, CardControl, CardAuthorization, CardTransaction, rainWebhook.
Card Ops
Convert network events into ledger holds, clearing postings, settlement records, and reconciled operational truth.
AuthorizationHold, ClearingRecord, SettlementBatch, ReconciliationRun, ReconException.
Ops Controls
Resolve exceptional money movement with policy, evidence, customer communication, and audit-safe control actions.
PaymentException, RefundDecision, CardDispute, ControlAction, OpsCase, OpsIncident.
Testing & Sandbox
Simulate API lifecycles, provider events, failure modes, webhook delivery, retries, and go-live readiness.
SandboxProject, TestFixture, ScenarioRun, WebhookEndpoint, WebhookAttempt, ReplayJob.
Money Journey
Explain where value, risk, ledger entries, customer state, provider obligations, and finance truth move end to end.
MoneyJourney, ValueState, LedgerMovement, ProviderObligation, FinanceEvent.
Provider Adapters
Hide provider-specific commands, payloads, webhooks, errors, and credentials behind stable internal contracts.
ProviderAdapter, AdapterCommand, ProviderWebhook, MappingRule, HealthCheck.
Fiat & Local Rails
Route local collections and payouts through country rails, local providers, banks, cutoffs, returns, and settlement reports.
FiatRoute, FiatCollectionIntent, FiatPayment, FiatPayout, ProviderObligation, FiatReconciliationRun.
Ops Playbooks
Turn incidents, exception handling, escalation paths, and glossary definitions into repeatable operating practice.
Playbook, RunbookStep, EscalationPolicy, GlossaryTerm, Postmortem.
API Security
Protect every command and event with scoped access, idempotency, signatures, approvals, and audit evidence.
ApiKey, ServiceToken, Scope, IdempotencyRecord, WebhookSignature, AuditLog.
Event Catalog
Define event producers, consumers, payloads, versions, retries, replay rules, and operational ownership.
EventType, EventSchema, EventDelivery, ReplayJob, ConsumerSubscription.
Data Model
Connect product objects to custody, customer ledger accounts, transactions, cases, and reconciliation records.
CustomerLedgerAccount, CustodyWallet, LedgerEntry, ProductResource, ReconciliationLink.
Treasury Settlement API
Custody, ledger, mint, burn, optional staking, and pay out value through crypto or fiat rails.
LedgerAccount, Deposit, MintRequest, BurnRequest, YieldAllocation, FxQuote, Payout.