Implementation Engineer

About Flex

Flex was founded to solve a simple but costly problem: making it easy for health and wellness brands to accept HSA and FSA payments online. For years, only giants like Amazon and Walmart could process these payments at checkout, leaving smaller merchants — and their customers — to deal with frustrating reimbursement paperwork.

Our technology verifies product eligibility in real time, handles split payments for eligible and non-eligible items, and can even issue Letters of Medical Necessity during checkout. With $150 billion in annual HSA/FSA spending potential, we’re giving brands the tools to unlock new revenue and making it easier for consumers to use the benefits they’ve earned.

About the Role

We’re looking for a contract Implementation Engineer to support merchant onboarding and technical integrations. This role sits at the intersection of Support Engineering, Product, and Customer Success, and is focused on helping partners successfully implement and launch our APIs and checkout flows.

This is a hands-on, execution-oriented role ideal for someone who enjoys working directly with customers, debugging real-world integration issues, and shipping solutions quickly in a fast-moving startup environment.

Mindset

• Low ego — open to feedback and growth.

• Collaborative — thrive in cross-functional team settings.

• Hustler — put in the effort required to make things happen.

• Self-starter — quick to learn new technologies and skills.

What You’ll Do

• Support merchants during onboarding and implementation of our APIs and checkout solutions

• Troubleshoot integration issues related to APIs, webhooks, authentication, and payment flows

• Review and validate API requests/responses using tools like Postman and logs

• Assist merchants with setup across platforms (e.g., custom integrations, e-commerce platforms)

• Debug issues related to subscriptions, payments, webhooks, and data mismatches

• Partner closely with Support Engineering, Product, and Engineering to escalate bugs and unblock launches

• Help document common implementation patterns, FAQs, and known issues

• Occasionally assist with light data validation or configuration updates in internal tools

What We're Looking For

• 2+ years of experience in an implementation, support engineering or customer engineering

• Comfortable working with REST APIs, JSON, and HTTP requests

• Experience using Postman (or similar tools) to test and debug APIs

• Familiarity with webhooks and asynchronous event flows

• Strong troubleshooting and problem-solving skills

• Clear, empathetic written communication — you’ll be working directly with external partners

• Ability to work independently, prioritize tasks, and manage multiple implementations at once

• Experience in Shopify implementation

Nice to Haves

• Experience supporting payment systems, subscriptions, or checkout flows

• Familiarity with Stripe, Shopify, or other e-commerce platforms

• Experience in a startup or high-growth environment

• Light SQL or data-debugging experience

• Previous experience working with customer-facing technical roles

Contract Details

• Independent Contractor (1099) role, fixed-term

• Flexible hours, with some overlap with U.S. business hours preferred

• Fully remote

• Opportunity to extend or convert based on business needs and performance

Why This Role?

You’ll play a critical role in getting partners live and successful, while working closely with a small, collaborative team. This role is ideal for someone who likes being close to real customer problems and seeing the direct impact of their work.

Flex is a remote-first team with quarterly in-person meetups. We are an equal opportunity employer and encourages applicants from all backgrounds and life experiences. We celebrate diversity and do not discriminate based on race, religion, color, national origin, sexual orientation, gender identity, gender expression, age, veteran status, disability status, or any other legally protected characteristic.