How Shopify Payments works

How Flex Shopify Payment App works

Checking out with Flex

Once the app is installed "Flex | pay with HSA/FSA" will show up as one of the payment options during checkout. When selected Shopify will send a request to Flex to generate a checkout session to redirect the user to. As part of generating the checkout session, Flex will check all the items in the customer's cart and determine it's eligibliity.

The items in the cart can fall under one of the following:

All items are HSA/FSA eligible

All items in their cart are HSA/FSA eligible either through Auto Substantiation or a Letter of Medical Necessity. The customer will be presented with a banner informing them that all items are eligible and to proceed with the HSA/FSA card.

Some items are HSA/FSA eligible

Some of the items in their cart are HSA/FSA eligible and the remaining items are not. We refer to this scenario as a split cart. In a split cart the customer is prsented with a banner letting them know that some items are eligible while the remaining are not. They will be prompted for their HSA/FSA card to pay for the items that are eligible and their credit card for the items that are not eligible.

The steps for a split cart are:

  1. Place a temporary hold on the HSA/FSA payment for the HSA/FSA eligible amount.
  2. Process the credit/debit card for the non eligible amount.
  3. Capture the HSA/FSA funds that were placed on hold.
  4. Redirect to the shopify order completion page.

On the shopify side, this appears as a single order.

Not eligible

None of the customer's items in the cart have been deemed as HSA/FSA eligible. A banner is presented to the customer letting them know that none of the items in their cart are HSA/FSA eligible and will be prompted to proceed with their credit card to complete their purchase.

Flex optimizes for conversion which is why we prompt the user to proceed with their credit card. Our research indicates directing the customer to start the checkout session process all over again does not convert as well as prompting them for a credit card.


When a customer checks out with Flex you'll see the order processed just as it would be for any other payment method. The only difference is in the order details page, the payment gateway specified will be "Flex".