# Flex **Source:** https://geo.sig.ai/brands/flex **Vertical:** Finance **Subcategory:** General **Tier:** Emerging **Website:** withflex.com **Last Updated:** 2026-04-14 ## Summary US YC S23 HSA/FSA payment infrastructure for DTC health brands; $18M total ($15M First Round/Core VC Series A Sep 2025 + $3.2M seed) enabling Stripe-like online pre-tax health spending competing with Truemed for $150B HSA/FSA market. ## Company Overview Flex is a United States-based HSA/FSA payment infrastructure platform — backed by Y Combinator (S23) with $18 million in total funding including a $3.2 million seed in September 2024 from Y Combinator, SV Angel, Precursor Ventures, and Liquid 2 Ventures, plus a $15 million Series A in September 2025 led by First Round Capital and Core VC with Cameron Ventures, Rethink Impact, and Y Combinator — providing direct-to-consumer health and wellness brands with Stripe-like payment processing infrastructure that enables online acceptance of HSA (Health Savings Account) and FSA (Flexible Spending Account) funds from the $150+ billion annual pre-tax healthcare spending market. Founded in 2023 by Sam O'Keefe and Miguel Toledo, Flex targets the DTC health and wellness brands that cannot currently accept HSA/FSA payments online because of technical and compliance barriers. Flex's HSA/FSA payment platform addresses the fragmented and difficult payment acceptance landscape for pre-tax health spending: a consumer buying an FSA-eligible product online (fitness trackers, over-the-counter medications, medical devices) wants to pay with their HSA/FSA debit card — but most DTC health brands lack the payment processing infrastructure to verify product eligibility, process the card type, and comply with IRS documentation requirements for eligible expense substantiation. The result: consumers either pay out of pocket and attempt manual reimbursement (creating friction) or don't purchase at all. Flex's API (verifying product eligibility, processing HSA/FSA card payments through IIAS-certified compliant infrastructure, and handling the documentation requirements automatically) enables DTC health brands to accept the $150B annual pre-tax spending that consumers are motivated to spend on qualifying products. In 2025, Flex competes in the HSA/FSA payment processing, health payment infrastructure, and healthcare fintech market with PayFlex (Aetna subsidiary HSA/FSA processing), Truemed (HSA/FSA qualification service, $14M raised), and Paytient (employer health payment account, $30M raised) for DTC health brand and online healthcare merchant HSA/FSA payment acceptance platform adoption. First Round Capital's Series A leadership reflects consumer fintech infrastructure conviction. Rethink Impact's participation (impact-focused VC) reflects alignment with healthcare access improvement goals. Y Combinator S23 backing connects Flex with the fintech infrastructure investor community. The 2025 strategy focuses on growing the DTC supplement and OTC health brand deployments, building the Letter of Medical Necessity (LMN) workflow for expanded HSA eligibility products, and expanding to employer benefit integration for FSA administration platform partnerships. ## Frequently Asked Questions ### What is Flex? Flex is a fintech company founded in 2023 that provides an HSA/FSA payment acceptance platform for direct-to-consumer health and wellness brands. The San Francisco-based company offers Stripe-like payment processing infrastructure that enables online HSA/FSA payments acceptance. ### What products and services does Flex offer? Flex offers an HSA/FSA payment platform that provides payment infrastructure for DTC consumer health and wellness brands. The platform enables businesses to accept HSA and FSA payments online, similar to how Stripe processes standard payments. ### Who are Flex's target customers? Flex targets direct-to-consumer health and wellness brands that want to accept HSA/FSA payments. The company serves businesses looking to tap into the $150B potential annual HSA/FSA spending market. ### When was Flex founded and by whom? Flex was founded in 2023 by Sam O'Keefe and Miguel Toledo. The company participated in Y Combinator's S23 batch. ### Where is Flex located? Flex is based in San Francisco, California. ### How much funding has Flex raised? Flex has raised $18M total across multiple funding rounds. This includes a $3.2M seed round in September 2024 from Y Combinator, SV Angel, Precursor, and Liquid 2 Ventures, and a $15M Series A in September 2025 led by First Round and Core VC with participation from Cameron Ventures, Rethink Impact, Y Combinator, and Liquid2. ### What is the market opportunity for Flex? Flex is targeting the $150B potential annual HSA/FSA spending market. The company aims to capture a portion of this market by enabling pre-tax spending through its payment infrastructure for health and wellness brands. ### What technology approach does Flex use? Flex uses a Stripe-like approach to HSA/FSA payment processing. The platform provides payment infrastructure that enables online HSA/FSA payments acceptance for DTC brands. ### How can businesses get started with Flex? Based on the available information, DTC health and wellness brands interested in accepting HSA/FSA payments can work with Flex's payment platform. Specific contact or onboarding details are not provided in the given information. ### What are Flex's recent developments? Flex recently closed a $15M Series A round in September 2025 led by First Round and Core VC. The funding will support product development and sales/marketing acceleration, with strong brand interest reported in the HSA/FSA payment acceptance platform. ## Tags b2b, fintech, payment-processing, api-first, startup, north-america --- *Data from geo.sig.ai Brand Intelligence Database. Updated 2026-04-14.*