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Implementation Engineer
contractUnited States

Summary

Location

United States

Type

contract

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About this role

Job Title

Implementation Engineer

Location

Remote (U.S. preferred)

Contract ( with potential to extend into full time)

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.

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 Have

  • 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

  • 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

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.

Other facts

Tech stack
API Implementation,Technical Integrations,Debugging,Postman,Webhooks,Authentication,Payment Flows,E-commerce Platforms,Troubleshooting,Customer Success,Support Engineering,REST APIs,JSON,HTTP Requests,Shopify Implementation,Data Validation

About Flex

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.

We love to hear your thoughts, comments and ideas so feel free to like, share and comment away. Any question or opinion is good to go as long as it is respectful and falls within the scope of this page. Derogatory comments, spam and unsolicited selling are not welcome here and such posts will be removed.

Industry: FinTech
Founding Year: 2019

Employee benefits

Equity compensation
Medical, dental and vision plans
Unlimited PTO and sick days
Parental leave

What you'll do

  • The Implementation Engineer will support merchants through the onboarding and technical implementation of APIs and checkout solutions, focusing on hands-on execution and debugging integration issues.

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Frequently Asked Questions

What does a Implementation Engineer do at Flex?

As a Implementation Engineer at Flex, you will: the Implementation Engineer will support merchants through the onboarding and technical implementation of APIs and checkout solutions, focusing on hands-on execution and debugging integration issues..

Why join Flex as a Implementation Engineer?

Flex is a leading FinTech company. They offer great benefits including Equity compensation, Medical, dental and vision plans, Unlimited PTO and sick days.

Is the Implementation Engineer position at Flex remote?

The Implementation Engineer position at Flex is based in United States, United States. Contact the company through Clera for specific work arrangement details.

How do I apply for the Implementation Engineer position at Flex?

You can apply for the Implementation Engineer position at Flex directly through Clera. Click the "Apply Now" button above to start your application. Clera's AI-powered platform will help match your profile with this opportunity and guide you through the application process. You can also learn more about Flex on their website.