Full-Stack Developer for SMRT GraphQL API Booking Integration Prototype

We are seeking an experienced full-stack/API integration developer to build a narrowly scoped technical prototype connecting a customer-facing booking flow to SMRT Systems through SMRT’s documented GraphQL Checkout API. This is a Backend-for-Frontend (BFF)-style integration. The goal of the first engagement is to prove that a secure server-side integration can reliably create a valid pickup appointment inside SMRT’s test environment. The prototype must demonstrate: - secure server-side authentication to SMRT - customer/address handling as required by the supported API - retrieval of real SMRT scheduling availability - creation of a valid pickup appointment - deterministic confirmation such as an appointment ID/status - verification that the appointment appears correctly inside SMRT - appropriate handling of retries, timeouts, and duplicate submissions - a proposed lightweight hosting/backend architecture - secure API-key handling with no credentials exposed in browser code SMRT must remain the operational system of record. We are not building a second appointment-management platform or replacing SMRT. The eventual solution should support two customer-facing brands through one maintainable codebase/configuration model rather than two separately developed applications. The fixed-price milestone is for a technical prototype only. A later customer-facing MVP may be commissioned separately if the prototype succeeds. Please review the attached Project 1B technical brief for full scope, deliverables, security/ownership requirements, and pricing expectations. Strong candidates should have experience with GraphQL APIs, third-party API integrations, backend/server-side development, transactional workflows, idempotency/duplicate prevention, cloud/serverless deployment, and logging/troubleshooting. Please provide separate estimates for: (A) the technical prototype, (B) a future customer-facing MVP, and (C) expected monthly hosting/infrastructure plus ongoing maintenance.