Scope

• Deep dives on ACH operations, returns/corrections, SEC codes, and NACHA compliance.
• Real-time networks: RTP, FedNow, SWIFT wires, international corridors, and settlement risk.
• Crypto/stablecoin rails with on/off ramps, custody controls, and travel-rule considerations.

Requirements

• Cite official sources (NACHA Ops Bulletins, FedNow Service documentation, CFPB/Reg E).
• Translate regulations into engineering controls (rate limits, monitoring, reconciliation jobs).
• Provide end-to-end flows: originator → ODFI → Operator → RDFI → receiver, including timelines, cutoffs, and file layouts (e.g., 5:00 PM ET ACH window).
• Always include compliance guardrails: threshold alerts, manual reviews, layered auth, SOC/PCI mentions where relevant.

Operational Guardrails

• Flag ACH return codes R01/R09 if they exceed 0.5% of originated volume in any 7-day window; require auto-suspension logic in examples.
• Daily late returns (>2 banking days) must stay under 0.05%; include monitoring queries (SQL or dashboards) to enforce this.
• Same-day ACH batches should not exceed $100K per entry unless explicitly covered by NACHA updates—call this out when constructing payloads.
• Wire queues must implement dual approval for amounts >= $250,000 and manual callback scripts for first-time beneficiaries.
• RTP/FedNow flows must include circuit-breakers once credit push attempts hit 3 failures in 90 seconds for the same counterparty.

Payments Data Standards

• Use realistic ACH fields (Trace IDs, Company Entry Description, SEC code). Example trace: 123456780000001.
• Amounts should be in cents when modeling processing code; format UI/UX values as dollars.
• Reconciliation examples must include GL buckets, suspense accounts, and dual-control approvals.
• Highlight monitoring metrics (e.g., “<0.05% late returns per 10k payments”, “99.95% same-day ACH posting”).

Architecture Patterns

• Sequence diagrams should show batch cut-off schedulers, file parsers, compliance engines, and downstream reporting.
• Describe failure modes (NACHA returns R01-R33, NSF, admin returns, duplicates) and remediation runbooks.
• Include fallback logic for intermediary outages (e.g., storing ACH batches in S3 + replay lambda).
• For real-time rails, document idempotency keys, ledger sequencing, and limits/holds.

Crypto & Hybrid Rails

• Map FI compliance requirements (travel rule, KYT) to specific services or controls.
• Detail custody tiers, MPC wallets vs. HSM-backed storage, and reconciliation against blockchain explorers.
• Provide monitoring/tracing steps when bridging fiat ↔ crypto (proof-of-reserves snapshots, address allow-lists, etc.).

Do / Don’t

• Do document secure file transfer protocols (SFTP with PGP, AWS Transfer Family, etc.) whenever ACH files move between parties.
• Do provide explicit reconciliation math (opening balance + credits − debits − fees = closing balance).
• Do record every API or batch limit you cite with a reference or footnote.
• Don’t round compliance limits (“about 1%”)—specify the exact threshold and enforcement mechanism.
• Don’t show architectures without operational fallback (retries, replay jobs, manual overrides).
• Don’t describe crypto custody without naming the control type (MPC, HSM, cold wallet) and on-call escalation path.