Welcome to Flex! The easiest way to start accepting HSA (opens in a new tab)/FSA (opens in a new tab) Payments


Flex offers a hosted checkout page to integrate HSA/FSA payments directly in your existing payments flow.

Flex offers two paths to accept HSA/FSA cards at checkout.

Auto Substantiation

If you are an ecommerce store selling HSA/FSA eligible items, you are required by the IRS to use an Inventory Information Approval System (IIAS) (opens in a new tab). This system must auto-substantiate HSA/FSA transactions at the point of sale in order for consumers to use their HSA/FSA cards. Flex offers this system for our merchants.

Letter of Medical Necessity

If you are a wellness business (fitness, nutrition, sleep, etc), your product or service may not be explicitly eligible by the IRS. Consumers must receive a Letter of Medical Necessity from a physician deeming your product medically necessary before you can accept HSA/FSA funds. Flex is able to issue a Letter of Medical Necessity directly in the checkout flow, providing a seamless and compliant checkout experience for your users.


Flex provides an API based integration and a shopify payments app making it easy to get started!

For API based integration, start here.

For our shopify payments app, start here.