Senior POS & Payments Engineer (Remote, Full-Time, 12+ Months)
Budget / SalaryHourly project
TypeFreelance project
LocationRemote
Posted1 hour ago
Senior POS & Payments Engineer (Remote, Full-Time, 12+ Months)
AMYN is hiring a remote senior engineer to build our point-of-sale and payments platform end to end: business logins, card processing, terminal hardware, the backend, and QuickBooks sync. Full-time for a minimum of 12 months, fully remote, with at least 4 hours a day of overlap with US business hours.
ABOUT THE ROLE
You will be the lead engineer on the AMYN payments and POS platform. Businesses sign up, log in, connect their card readers, printers and cash drawers, take payments, and see every sale flow into QuickBooks automatically. You will design, build and maintain that whole chain.
This is a hands-on role, not a management role. You will own architecture decisions, write most of the code, and work directly with the founder. We need someone who has already shipped a POS or payments product, not someone learning the domain on the job.
WHAT YOU'LL BUILD
1. Business logins and user management
- Multi-tenant accounts: every business has its own isolated data, locations, devices and settings.
- Owner and admin web login: email and password, two-factor authentication, password reset, session control.
- Roles and permissions: owner, manager, cashier, accountant, with access set per location.
- Fast employee login on the register: PIN or badge, clock in and out, manager approval for voids, refunds and discounts.
- Business onboarding: sign-up, KYC/KYB verification with the payment processor, and bank account setup for payouts.
- An audit log of who did what, on which device, and when.
2. Payment processing
- Integrate with processors or gateways such as Stripe Terminal, Adyen, Fiserv/Clover, TSYS, Worldpay, NMI or Authorize.net.
- In-person payments: EMV chip, tap (NFC, Apple Pay, Google Pay) and swipe fallback. Online and keyed payments, payment links and invoices.
- Authorize, capture, void, refunds, tips, split tender, split checks, and pre-auth for open tabs.
- Tokenization and point-to-point encryption so raw card data never touches our servers.
- Offline store-and-forward, batch close, settlement, payout reconciliation and chargeback handling.
- US sales tax rules, surcharging and cash-discount programs.
3. Connecting hardware to software
- Secure device pairing: link each terminal, reader or register to one business and location, and disable lost devices remotely.
- Card terminals: PAX, Ingenico, Verifone, Clover, Stripe readers, Sunmi Android POS.
- Peripherals: receipt and kitchen printers (Epson, Star Micronics, ESC/POS), cash drawers, barcode scanners, scales, customer displays, kitchen display screens.
- USB, Bluetooth, serial, LAN, Wi-Fi and cloud API connections, device monitoring, remote configuration and over-the-air updates.
4. Backend, dashboard and register apps
- APIs, webhooks and background jobs; data model for products, modifiers, inventory, orders, customers, discounts, gift cards, loyalty, taxes, employees and shifts.
- Web dashboard for business owners with sales and end-of-day reports.
- Register app on Android terminals and tablets, and on iPad.
- Cloud infrastructure, CI/CD, monitoring, backups and alerting, built for 99.9% uptime.
5. QuickBooks integration
- QuickBooks Online API with OAuth 2.0 connect for each business.
- Sync sales, payments, refunds, tips, processor fees, sales tax and deposits to the right accounts.
- Mapping screens, retries, duplicate prevention and a readable sync log. Designed so Xero can be added later.
MUST-HAVE EXPERIENCE
- 6+ years of software engineering, with 3+ years on POS, payments or fintech products in production.
- At least one shipped card processor or gateway integration that handled real transactions.
- Hands-on work with EMV terminals, receipt printers and cash drawers.
- Strong backend skills (Node.js/TypeScript, Python, Go, Java or C#), PostgreSQL or MySQL, Redis, REST APIs and webhooks.
- OAuth 2.0, JWT, two-factor authentication, role-based access control and multi-tenant design.
- A QuickBooks Online API integration you built or maintained.
- Android (Kotlin or Java) or React Native / Flutter for register apps.
- Working knowledge of PCI DSS, tokenization and encryption.
- Proven experience protecting production systems that handle payments or sensitive data, including a security audit or penetration test you helped pass.
- Secure coding against the OWASP Top 10, threat modeling, dependency scanning and fixing vulnerabilities.
- Cloud and network hardening: firewalls, private networks, least-privilege access, secrets and key management (KMS or HSM), and patching.
- Securing POS devices: locked-down Android terminals (kiosk mode or MDM), signed app updates and mutual TLS.
- Defending logins and payments against brute-force attacks, credential stuffing, card testing and fraud.
- Security monitoring and incident response: central logging, intrusion alerts, tested backups and a breach response plan.
- AWS, GCP or Azure, Docker and CI/CD.
- Clear written and spoken English.
- At least 4 hours a day of overlap with 9am to 5pm US Eastern time.
- Reliable internet and backup power.
PAY AND TERMS
- Pay: USD $2 per hour (about $350 per month full-time), paid through Freelancer.com
- Full-time, 40 hours a week, minimum 12-month commitment
- 30-day paid trial, counted as the first month of the 12-month term
- 12 paid days off a year plus your national public holidays
- We ship you a test card reader, receipt printer and cash drawer
- NDA and IP assignment agreement before you start
HOW TO APPLY
Start your bid with the word TERMINAL so we know you read this posting. Bids without it are not reviewed. Include links to POS or payments work you shipped, and short answers to:
1. Which payment processors or gateways have you integrated, and roughly how many transactions a month did they handle?
2. How would you securely pair a new card reader to one business and one location?
3. A card is approved on the terminal, but our server never receives the response. How do you prevent a double charge?
4. How would you sync one day of sales, tips, refunds and processor fees into QuickBooks Online so the bank deposit matches?
5. How do you keep a POS system's PCI DSS scope as small as possible?
6. Which terminals, printers and other POS hardware have you worked with directly?
AMYN is hiring a remote senior engineer to build our point-of-sale and payments platform end to end: business logins, card processing, terminal hardware, the backend, and QuickBooks sync. Full-time for a minimum of 12 months, fully remote, with at least 4 hours a day of overlap with US business hours.
ABOUT THE ROLE
You will be the lead engineer on the AMYN payments and POS platform. Businesses sign up, log in, connect their card readers, printers and cash drawers, take payments, and see every sale flow into QuickBooks automatically. You will design, build and maintain that whole chain.
This is a hands-on role, not a management role. You will own architecture decisions, write most of the code, and work directly with the founder. We need someone who has already shipped a POS or payments product, not someone learning the domain on the job.
WHAT YOU'LL BUILD
1. Business logins and user management
- Multi-tenant accounts: every business has its own isolated data, locations, devices and settings.
- Owner and admin web login: email and password, two-factor authentication, password reset, session control.
- Roles and permissions: owner, manager, cashier, accountant, with access set per location.
- Fast employee login on the register: PIN or badge, clock in and out, manager approval for voids, refunds and discounts.
- Business onboarding: sign-up, KYC/KYB verification with the payment processor, and bank account setup for payouts.
- An audit log of who did what, on which device, and when.
2. Payment processing
- Integrate with processors or gateways such as Stripe Terminal, Adyen, Fiserv/Clover, TSYS, Worldpay, NMI or Authorize.net.
- In-person payments: EMV chip, tap (NFC, Apple Pay, Google Pay) and swipe fallback. Online and keyed payments, payment links and invoices.
- Authorize, capture, void, refunds, tips, split tender, split checks, and pre-auth for open tabs.
- Tokenization and point-to-point encryption so raw card data never touches our servers.
- Offline store-and-forward, batch close, settlement, payout reconciliation and chargeback handling.
- US sales tax rules, surcharging and cash-discount programs.
3. Connecting hardware to software
- Secure device pairing: link each terminal, reader or register to one business and location, and disable lost devices remotely.
- Card terminals: PAX, Ingenico, Verifone, Clover, Stripe readers, Sunmi Android POS.
- Peripherals: receipt and kitchen printers (Epson, Star Micronics, ESC/POS), cash drawers, barcode scanners, scales, customer displays, kitchen display screens.
- USB, Bluetooth, serial, LAN, Wi-Fi and cloud API connections, device monitoring, remote configuration and over-the-air updates.
4. Backend, dashboard and register apps
- APIs, webhooks and background jobs; data model for products, modifiers, inventory, orders, customers, discounts, gift cards, loyalty, taxes, employees and shifts.
- Web dashboard for business owners with sales and end-of-day reports.
- Register app on Android terminals and tablets, and on iPad.
- Cloud infrastructure, CI/CD, monitoring, backups and alerting, built for 99.9% uptime.
5. QuickBooks integration
- QuickBooks Online API with OAuth 2.0 connect for each business.
- Sync sales, payments, refunds, tips, processor fees, sales tax and deposits to the right accounts.
- Mapping screens, retries, duplicate prevention and a readable sync log. Designed so Xero can be added later.
MUST-HAVE EXPERIENCE
- 6+ years of software engineering, with 3+ years on POS, payments or fintech products in production.
- At least one shipped card processor or gateway integration that handled real transactions.
- Hands-on work with EMV terminals, receipt printers and cash drawers.
- Strong backend skills (Node.js/TypeScript, Python, Go, Java or C#), PostgreSQL or MySQL, Redis, REST APIs and webhooks.
- OAuth 2.0, JWT, two-factor authentication, role-based access control and multi-tenant design.
- A QuickBooks Online API integration you built or maintained.
- Android (Kotlin or Java) or React Native / Flutter for register apps.
- Working knowledge of PCI DSS, tokenization and encryption.
- Proven experience protecting production systems that handle payments or sensitive data, including a security audit or penetration test you helped pass.
- Secure coding against the OWASP Top 10, threat modeling, dependency scanning and fixing vulnerabilities.
- Cloud and network hardening: firewalls, private networks, least-privilege access, secrets and key management (KMS or HSM), and patching.
- Securing POS devices: locked-down Android terminals (kiosk mode or MDM), signed app updates and mutual TLS.
- Defending logins and payments against brute-force attacks, credential stuffing, card testing and fraud.
- Security monitoring and incident response: central logging, intrusion alerts, tested backups and a breach response plan.
- AWS, GCP or Azure, Docker and CI/CD.
- Clear written and spoken English.
- At least 4 hours a day of overlap with 9am to 5pm US Eastern time.
- Reliable internet and backup power.
PAY AND TERMS
- Pay: USD $2 per hour (about $350 per month full-time), paid through Freelancer.com
- Full-time, 40 hours a week, minimum 12-month commitment
- 30-day paid trial, counted as the first month of the 12-month term
- 12 paid days off a year plus your national public holidays
- We ship you a test card reader, receipt printer and cash drawer
- NDA and IP assignment agreement before you start
HOW TO APPLY
Start your bid with the word TERMINAL so we know you read this posting. Bids without it are not reviewed. Include links to POS or payments work you shipped, and short answers to:
1. Which payment processors or gateways have you integrated, and roughly how many transactions a month did they handle?
2. How would you securely pair a new card reader to one business and one location?
3. A card is approved on the terminal, but our server never receives the response. How do you prevent a double charge?
4. How would you sync one day of sales, tips, refunds and processor fees into QuickBooks Online so the bank deposit matches?
5. How do you keep a POS system's PCI DSS scope as small as possible?
6. Which terminals, printers and other POS hardware have you worked with directly?
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