Embedded Finance & Treasury
The treasury layer your vertical SaaS deserves.
Sub-ledger engine, FBO accounts, ACH/RTP/FedNow rails, and KYB onboarding — pre-assembled as a single REST API. For vertical SaaS founders who want the treasury feature, not the compliance program to run it.
Platform
Every piece of treasury infrastructure, pre-assembled.
Sub-Ledger Engine
Multi-entity ledger that tracks balances, transactions, and reconciliation across every platform using your SaaS.
FBO Account Structure
For-benefit-of accounts held at our bank partner. Your platforms hold customer funds legally, without a bank charter.
ACH, RTP & FedNow Rails
Same-day ACH, real-time payments via RTP and FedNow. One API surface, three rails, your platform picks the speed.
KYB Onboarding
Know-Your-Business checks for every SMB on your platform. Reg-compliant identity verification with minimal friction.
REST API + Webhooks
Full-featured REST API with idempotent endpoints, webhook event streams, sandbox environment, and client libraries.
Compliance Layer
Reg E dispute handling, BSA/AML program, NACHA compliance. We run the compliance infrastructure; your team runs the product.
Verticals
Built for the platforms that serve Main Street.
Fitness & Wellness
Studio management platforms need ACH payouts for instructors and membership fee collection.
See how it works →Home Services
HVAC and lawn care platforms need fast job payment disbursement to contractors.
See how it works →Beauty & Salon
Nail salon and spa platforms handle staff tip pooling and product purchasing at scale.
See how it works →Veterinary
Vet clinic platforms manage deposit holds, payment plans, and insurance reconciliation.
See how it works →Field Services
Contractor management platforms need real-time payment rails for job completion payouts.
See how it works →Integration
Live in weeks, not quarters.
Connect Your SaaS
Install the Mainstreetspine SDK (Node, Python, Ruby). Point it at your existing user/platform data model. Takes an afternoon.
Provision Your Platforms
Each SMB on your platform gets a virtual account number and FBO sub-account. KYB runs in the background. No manual review queue.
Launch Treasury Features
Enable ACH payouts, same-day transfers, account balances — as features in your existing UI. Revenue share starts day one.
Payment Rails
All three payment rails. One integration.
ACH for bulk payroll runs. RTP for instant invoice settlements. FedNow for government-connected clients. Your platform never needs to think about rail selection — we route by speed and cost automatically.
Explore the PlatformFrom our partners
What platform builders say
We evaluated Unit and Modern Treasury. Mainstreetspine was the only one that understood we serve HVAC contractors, not enterprise developers. Their KYB flow is tuned for SMBs.
Marcus Webb
CTO — Fieldwork SaaS (field services platform)
Getting FBO accounts set up at our bank used to mean 6 months of negotiations. Mainstreetspine had us live with virtual accounts in three weeks. The rev-share model made the CFO decision easy.
Priya Anand
Co-founder & CPO — StudioPulse (fitness management SaaS)
Ready to add treasury to your SaaS?
Talk to Devon and the team. We work with a small number of vertical SaaS partners at a time — each integration gets hands-on attention.
Request a Pilot