
Implementation Engineer
Remote (U.S. preferred)
Contract ( with potential to extend into full time)
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.
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
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
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 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
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.
About Flex
Flex enables businesses to accept HSA/FSA payments, unlocking the $120B sitting in these accounts. We're on a mission to make health more accessible.
Flex enables businesses to accept HSA/FSA payments, unlocking the $120B sitting in these accounts. We’re an early stage startup backed by Y-Combinator, SV Angel, Liquid2, and Precursor Ventures, with angels from Stripe, Shippo, Unit21, and OpenAI. We ascribe to Netflix’s “Dream Team” culture and strive for every team member to be exceptional in their role and as teammates. Our team is remote across US time zones with quarterly in person meetups. Given this, the ability to operate autonomously is an absolute must.
We’re the manufacturing partner of choice that helps a diverse customer base design and build products that improve the world.
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