Senior Integration Engineer (Python/REST/GraphQL/Shopify/BigQuery)

NO AGENCIES. INDEPENDENT FREELANCERS ONLY. READ THIS FIRST: This is backend integration engineering: API contracts, OAuth, webhooks, data reconciliation between enterprise platforms. It is not storefront, theme or Liquid work. If your ecommerce experience is building and styling storefronts, do not apply. You will carry the heaviest share of the Shopify, POS and OMS integration work: building the connections between platforms and owning the data that moves through them. Full-time, long-term engagement. Key Responsibilities: • Build and maintain REST and GraphQL integrations with Shopify, POS, OMS and third-party business applications • Implement OAuth flows, webhook verification and processing, retries, deduplication and error handling for production data flows • Develop new API integrations with enterprise and SaaS platforms as the program expands • Own SQL and BigQuery work wherever integrations require data movement or transformation • Build reconciliation checks so systems of record stay in agreement • Troubleshoot production integrations and data quality issues • Contribute to shared integration services and frameworks Requirements: • 5+ years of backend engineering focused on API integrations between enterprise or SaaS platforms • Strong Python in production (will be tested during screening) • REST and GraphQL integration experience on both consuming and building sides • OAuth, API authentication, webhooks, and robust error handling patterns • Strong SQL; hands-on data integration or ETL experience • AWS deployment experience with Docker and CI/CD • Fluent English • Minimum 4 hours daily overlap with US Eastern time, full-time availability Nice to Have: • Google BigQuery • Shopify APIs (Admin GraphQL, webhooks, Fulfillment Orders) or SFCC OCAPI/SCAPI • POS, OMS, ERP or fulfillment system integration experience • Event-driven integration patterns: queues, event buses, connectors