Platform

The Mainstreetspine treasury stack.

Sub-ledger engine, FBO account structure, ACH/RTP/FedNow rails, KYB onboarding, and compliance program — five components that would take a SaaS team 12–18 months to negotiate and build separately, shipped as a single REST API integration.

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3 payment rails unified
<5 min virtual account provisioning
BSA/AML compliance program included
Weeks typical integration timeline

Capabilities

Everything your platform needs to hold and move money.

Sub-Ledger Engine

Double-entry bookkeeping across every entity. Supports multi-tenant, multi-currency schemas.

FBO Account Structure

Legally compliant for-benefit-of accounts. No bank charter needed for your team.

ACH, RTP & FedNow

All three rails, auto-routed by speed and cost. Same-day ACH, instant RTP and FedNow.

KYB Onboarding

Business identity verification tuned for SMBs, not enterprise onboarding flows.

REST API + Webhooks

Idempotent endpoints, event webhooks, sandbox environment, multi-language SDKs.

Compliance Layer

Reg E disputes, BSA/AML program, NACHA adherence — we maintain the program.

Sub-Ledger Engine

The accounting layer your platform never has to build.

Every dollar that moves through your platform needs a corresponding ledger entry — and those entries need to reconcile against your FBO pool balance, pass end-of-day settlement, and survive a bank exam. Our sub-ledger handles debit/credit pair creation, automated reconciliation, and balance tracking across every SMB sub-account in real time, with an immutable audit trail for every posted entry.

  • Double-entry bookkeeping per entity
  • Configurable chart of accounts per vertical
  • Real-time balance queries via API
  • Automated end-of-day reconciliation reports
  • Immutable audit trail for every transaction
Mainstreetspine platform architecture diagram showing sub-ledger engine connected to FBO accounts, virtual accounts, and ACH/RTP payment rails
POST /v1/virtual-accounts
{
  "platform_id": "plt_8xHQ2mNk",
  "entity_ref": "smb_glenwood-hvac",
  "type": "checking",
  "kyb_verified": true
}

// Response (201)
{
  "id": "va_HQ2mNk9r",
  "account_number": "826041200412",
  "routing_number": "021000021",
  "status": "active"
}

Virtual Accounts

A real account number for every SMB on your platform.

Each business using your SaaS gets a unique virtual account number — backed by a real FBO sub-account — provisioned in under five minutes via API. No paperwork, no bank branch visits.

  • Unique routing + account number per entity
  • Instant provisioning on KYB approval
  • Accept ACH credits, initiate ACH debits
  • Balance webhooks on every transaction

Payment Rails

One integration. All three rails.

Pass a single payment request to the Mainstreetspine API. We select the optimal rail based on your configured priority rules — speed, cost, or recipient bank availability.

ACH Standard

2–3 business day settlement. Lowest cost per transaction. Best for regular payroll disbursements and recurring transfers.

ACH Same-Day

Same-business-day settlement (up to 3 windows). Ideal for job completion payouts and end-of-day disbursements.

RTP (Real-Time Payments)

Instant final settlement 24/7/365. Per-transaction fee. Best for invoice settlements and on-demand contractor payouts.

KYB Onboarding

Business verification built for SMBs, not enterprise.

Most KYB providers are designed for enterprise onboarding — high-touch, document-heavy flows that work for a bank's commercial lending team but create abandonment when an HVAC contractor or nail salon owner tries to complete them on a mobile phone. We built our KYB flow specifically for the SMB contexts your vertical SaaS serves: EIN verification, beneficial ownership collection, and OFAC screening with conversion rates tuned for the small business owner, not the CFO.

  • EIN, business name, and beneficial ownership verification
  • Automated OFAC and sanctions screening
  • Exception queue with human review SLA
  • Webhook notifications on status changes
  • Re-verification workflow for expired documents

FBO Structure

Hold customer funds legally. No bank charter required.

FBO (For Benefit Of) accounts are how vertical SaaS platforms hold customer funds legally without a money transmitter license or bank charter. Our bank partner holds the omnibus FBO account; each SMB on your platform holds a segregated sub-account tracked by the sub-ledger. FDIC pass-through coverage applies to the pooled balance. The legal structure, bank relationship, and daily reconciliation are ours to maintain — not yours.

  • Fully segregated sub-account per SMB
  • FDIC pass-through coverage on pooled FBO
  • Daily reconciliation reports to your team
  • Managed by our bank partner relationship

Compliance

We run the compliance program. You run the product.

Banking compliance is complex and the failure modes are expensive. Mainstreetspine manages the regulatory program so your engineering team doesn't have to. We're not Stripe — we're the treasury infrastructure layer your vertical SaaS embeds for end-customer accounts, with BSA/AML, Reg E, and NACHA compliance maintained at the infrastructure level, not delegated back to you.

BSA/AML
NACHA Rules
Reg E Disputes
OFAC Screening

Ready to see the platform in action?

We run a 30-minute technical walkthrough for engineering and product teams evaluating embedded treasury. No sales pitch — just the stack.

Request a Pilot View API Docs