Developers

A REST API built for embedded treasury at scale.

Idempotent endpoints, HMAC-signed webhooks, full sandbox environment, and client libraries for Node, Python, and Ruby. Virtual account provisioning, sub-ledger operations, KYB submission, and multi-rail payment initiation — all through a single versioned REST API.

View Quickstart API Reference

const mss = require('mainstreetspine-node');
const client = new mss.Client({
  apiKey: process.env.MSS_API_KEY
});

const account = await client.virtualAccounts.create({
  platform_id: 'plt_8xHQ2mNk',
  entity_ref: 'smb_glenwood-hvac',
  type: 'checking'
});

console.log(account.account_number);
// → '826041200412'

API Overview

Five resource groups. One consistent API.

01 / virtual-accounts

Virtual Accounts

Create, read, and manage virtual account numbers for platform entities. Balance queries, transaction history, account status.

02 / payments

Payments

Initiate ACH, RTP, and FedNow transfers. Rail selection, idempotency keys, payment status polling.

03 / kyb

KYB Onboarding

Submit business verification requests. Poll status, handle exceptions, retrieve KYB decision details.

04 / ledger

Sub-Ledger

Query ledger entries, create manual journal entries, retrieve account statements, reconciliation exports.

05 / webhooks

Webhooks

06 / platforms

Platform Config

Manage platform-level settings, API keys, sandbox/live environment switching, revenue share reporting.

Quickstart

From API keys to first virtual account in 15 minutes.

Get API Keys

Request pilot access. We provision sandbox API keys within one business day of approval.

Install SDK

npm install mainstreetspine-node or pip install mainstreetspine. Initialize with your API key.

Create a Platform

POST /v1/platforms — register your SaaS platform as the parent entity in our system.

Provision a Virtual Account

POST /v1/virtual-accounts — your first sandbox account number is ready in under 5 minutes.

Read Full Quickstart

SDKs

Client libraries for your stack.

Node.js

mainstreetspine-node v1.4.2

Python

mainstreetspine v1.3.0

Ruby

mainstreetspine-ruby v1.2.1

REST API

Any HTTP client

Webhooks

Real-time event notifications for every state change.

Register a webhook endpoint. We'll POST signed JSON events to your server within 200ms of each state change. Automatic retry with exponential backoff on failed deliveries.

virtual_account.createdNew virtual account provisioned and ready to receive funds

payment.completedACH/RTP/FedNow payment settled successfully

payment.failedPayment failed — includes reason code and retry recommendation

kyb.approvedBusiness entity passed KYB verification

kyb.pending_reviewKYB sent to manual review queue — ETA included

ledger.entry.createdNew debit or credit entry posted to the sub-ledger

Webhook Documentation

Sandbox environment included.

All pilot partners get access to a full-featured sandbox with simulated ACH and RTP settlement, KYB verification flows, sub-ledger posting, and webhook delivery. Test your entire integration before a single live transaction touches the rails.

Request API Access