The Mainstreetspine platform
A full embedded finance API stack for vertical SaaS
Sub-accounts, virtual cards, ACH payouts, real-time ledger, and revenue-based credit — compliance and banking infrastructure handled end-to-end so your engineers build the product, not the rails.
The problem
Your merchants need financial tools your platform cannot build fast enough
Founders and engineering leads at vertical SaaS companies serving SMB merchants — restaurants, contractors, service businesses — know their customers need embedded finance. Accounts, cards, payments, and lending are table stakes for retaining high-value merchants. But building compliant treasury rails, KYC flows, and ledger infrastructure from scratch takes 18 to 24 months and requires hiring a specialized fintech team most vertical SaaS companies cannot afford or attract.
The result: platforms defer the financial features their best merchants ask for. Merchants churn to platforms that have already built them. The window for capturing embedded finance revenue narrows every quarter a platform waits.
How it works
API integration to live financial features in weeks
Mainstreetspine connects to your existing SaaS infrastructure via REST API. Your platform engineers do not build banking logic — they call Mainstreetspine endpoints and get back merchant financial primitives that plug into your product UI. The treasury engine, compliance layer, and banking partner relationships are managed entirely by Mainstreetspine.
Your platform connects via REST API using your existing SaaS customer database. Mainstreetspine ingests merchant identity, transaction history, and platform metadata via secure webhook integration — no schema migration required on your side.
The Mainstreetspine treasury engine provisions per-merchant sub-accounts, routes ACH and card transactions through partner banking rails, applies real-time ledger entries, and evaluates working capital eligibility via alternative-data credit models.
Platform operators receive a white-labeled embedded finance layer — merchant wallets, virtual cards, ACH transfers, revenue-based credit lines, and a real-time ledger — accessible via dashboard and API, without requiring a banking license or compliance team.
Platform modules
Six production-ready modules, one integration
Each module is available independently via API or as a bundled platform. You choose which features to expose to your merchants based on your product roadmap and merchant segment.
Sub-Account Provisioning
Spin up a compliant merchant account in under 60 seconds via API
Every merchant on your platform gets an FDIC-insured sub-account provisioned through our banking partner rails. KYC, AML, and BSA compliance are handled automatically so your engineering team never touches financial regulation. Accounts are accessible via API and white-labeled dashboard within your existing platform experience — zero redirect friction for your end users.
Virtual Card Issuance
Issue branded virtual debit cards to merchants instantly with full spend controls
Merchants receive a Mainstreetspine-powered virtual Visa or Mastercard card that can be used for business purchases immediately after KYC. Platform operators set spend category rules, velocity limits, and merchant-category block lists via the admin API. Cards are managed in-app — no physical card program overhead or BIN sponsorship complexity.
Embedded ACH & Payouts
Same-day ACH and instant payouts from merchant wallets to any US bank
Move money reliably with same-day ACH settlement and optional instant payout rails. Merchants pull earned revenue from their platform wallet to their business bank account on demand. Platform operators collect split-payment revenue automatically without manual reconciliation — all transactions are recorded in the real-time ledger with full audit trail.
Revenue-Based Credit Lines
Offer working capital to your best merchants using real transaction data
The Mainstreetspine credit engine evaluates merchant transaction history, revenue velocity, and platform tenure to pre-qualify merchants for working capital lines of $5K–$250K. Credit decisions happen in hours, not weeks, using alternative data instead of FICO. Platforms earn a revenue-share on deployed capital without taking credit risk — we hold the balance sheet.
Real-Time Ledger
Double-entry ledger with instant reconciliation and API-accessible transaction history
Every debit, credit, transfer, and fee is posted to a double-entry ledger in real time. Merchants and platform operators see accurate running balances and transaction histories without end-of-day batch delays. Export to QuickBooks, Xero, or any accounting system via webhook or scheduled CSV. Audit trails are immutable and regulator-ready from day one.
Compliance Automation
KYC, AML, and SAR filing handled automatically so you never need a compliance hire
Mainstreetspine wraps banking compliance into the onboarding flow — identity verification, watchlist screening, business entity validation, and ongoing transaction monitoring happen behind the API. Suspicious activity flags and SAR filings are managed by our compliance team in partnership with our sponsor bank. Your platform ships financial features without a compliance officer on staff.
Integrations
Works with the tools your platform already uses
Mainstreetspine connects to the infrastructure your platform and your merchants already rely on — no rip-and-replace required.
Who this is for
Built for vertical SaaS platforms at a specific stage
Mainstreetspine is not a horizontal banking-as-a-service product. It is purpose-built for vertical SaaS platforms whose merchant customers already rely on the platform for core operations and are ready to use it for financial services too.
Built for
Series A to early-B vertical SaaS founders and CTOs whose platforms serve SMB merchants — restaurant operators, contractors, or service businesses — and want to offer embedded banking, cards, or working capital as a product feature. Typically 15 to 150 employees, $2M to $20M ARR, with 500 to 10,000 active merchants processing $500K to $50M in annual payment volume.
Not for
Consumer fintech applications, standalone neobanks building their own chartered banking infrastructure, large enterprise treasury systems with existing compliance teams, or platforms operating outside the US market. Mainstreetspine is a US-market product requiring US banking partner rails and regulatory coverage.
See it in practice
Ready to review the API documentation?
Talk to a Mainstreetspine platform engineer who will walk you through integration, compliance flow, and time-to-first-payout estimates for your specific merchant segment.