Modern Treasury
Modern Treasury Technical Briefing
Published June 14, 2022
Supported by Modern Treasury , IowaEDA and Brale
Overview
Koji, PM at Modern Treasury, walks through Modern Treasury Ledgers — a managed double-entry ledger API for fintechs like Revolut and Marqeta, marketplaces like ClassPass and Outdoorsy, and anyone building money-movement apps. The demo builds out "BillFold," a sample digital wallet, and walks through the patterns Modern Treasury has seen in production: custom ISO currencies (including USDC with a six-digit exponent for stablecoin-native apps), pending-vs-posted states for in-flight payments, immutable pending transactions with full audit trails, combined payment-plus-ledger API calls, and optimistic locking for just-in-time card funding flows alongside card issuers like Lithic and Marqeta. The closing pattern — purely in-ledger transactions between user accounts — makes user-to-user transfers essentially instant without ever touching an external rail.
0:00 Introduction to Modern Treasury Ledgers
Koji, PM at Modern Treasury, introduces the Modern Treasury Ledgers API — a managed double-entry ledger for fintechs like Revolut and Marqeta, marketplaces like ClassPass and Outdoorsy, and anyone building money-movement apps.
1:00 Creating a ledger object (custom USDC currency)
Live walk-through of creating a Modern Treasury ledger in the dashboard (and the public API docs), including a custom USDC currency with a six-digit exponent for stablecoin-native apps.
2:00 The BillFold demo wallet — accounts and balances
A sample wallet app called BillFold is used to show core ledger objects — user ledger accounts, a cash account, and a card settlement account — and the posted vs pending balances tracked on each.
2:30 Double-entry ledger transactions
Why every money movement in the ledger has matching credits and debits — the pattern good fintechs use, whether the movement happens inside the app (user-to-user) or across external rails.
3:30 Pending vs posted — modelling money in flight
How Modern Treasury models payments as pending before they settle and posted after, so ACH in-transit or card authorizations are tracked accurately before they clear.
4:30 Combined payment-and-ledger API call
A Postman walk-through of payment orders: Jane deposits money into BillFold. One API call moves funds between bank accounts and writes the matching ledger entries, with an external_id for idempotency.
5:30 Immutable pending transactions + audit trail
Pending Modern Treasury ledger transactions are immutable with a full audit trail — so card-authorization amount changes are captured as edits rather than overwrites and the full history is reconstructable.
6:30 Just-in-time card funding with Lithic / Marqeta
The common pattern of using Modern Treasury Ledgers to manage card balances in real time alongside card issuers like Lithic and Marqeta — authorizing swipes against the ledger, then posting once the card network confirms.
7:30 Optimistic locking for card race conditions
How the ledger avoids race conditions on high-throughput card flows: each account read returns a locked version, which the subsequent transaction must reference; the write only succeeds if the version hasn't moved.
Presented by Koji Murase — Modern Treasury · LinkedIn · website
Topics: Payments, Treasury, Developer Tools
