Senior React Native / Bitcoin Lightning Engineer — Breez SDK

BitRelay is a Bitcoin-first payments application designed around a simple goal: Send Bitcoin as easily as sending a text. We are seeking a senior React Native / payments engineer to help complete BitRelay v1.0 and bring an existing founder-built codebase to a production-ready release candidate. This is NOT a greenfield project and you are NOT being hired to redesign the product from scratch. BitRelay already has defined product architecture, UX direction, payment behavior, fee rules, security requirements, technical specifications, and acceptance criteria. Your role will focus on implementation, integration, testing, failure-state hardening, and production-readiness engineering. CORE RESPONSIBILITIES • Integrate and harden the Breez SDK Spark React Native implementation using @breeztech/breez-sdk-spark-react-native. • Implement self-custodial Bitcoin wallet functionality, including send, receive, balance, transaction history, and recovery flows. • Implement durable transaction-state persistence capable of surviving app termination, network loss, duplicate callbacks, SDK timeouts, and interrupted execution. • Build asynchronous payment state machines with strong idempotency and reconciliation guarantees. • Implement the approved BitRelay @handle / recipient-resolution payment experience. • Help implement passkey-based authentication while maintaining strict separation between BitRelay account authentication and Bitcoin signing authority. • Develop and harden supporting TypeScript / Node.js backend services. • Build and test provider-neutral integration interfaces for optional KYC, buy/sell, and fiat functionality. • Create automated tests for normal and adversarial payment states. • Help bring the existing application through security hardening and release-candidate QA. IMPORTANT PAYMENT ARCHITECTURE REQUIREMENT BitRelay separately tracks: 1. The user's principal Bitcoin payment 2. BitRelay's service-fee obligation A successfully settled principal payment must NEVER be reversed, duplicated, or replayed merely because service-fee collection fails, times out, or remains unresolved. The application must durably persist payment state and reconcile ambiguous outcomes after crashes, restarts, network interruptions, or delayed SDK responses. REQUIRED EXPERIENCE We are looking for an engineer with strong experience in several of the following: • React Native • TypeScript • iOS and Android production applications • Node.js backend development • Bitcoin • Lightning Network • Breez SDK / Spark, LDK, or similar embedded Bitcoin wallet technology • BOLT11 • LNURL / Lightning Addresses • asynchronous payment systems • durable transaction state machines • idempotency • payment reconciliation • secure local storage • passkeys / WebAuthn • background processing • REST APIs • relational databases / SQLite • automated testing • CI/CD • fintech or payment infrastructure Experience with Breez Spark specifically is highly desirable. Generic Web3, Solidity, NFT, token, or DeFi experience alone is not sufficient for this engagement. MANDATORY APPLICATION QUESTION Please begin your proposal by answering this technical scenario: "In BitRelay's design, the principal Bitcoin payment and BitRelay's service-fee obligation are separately tracked transactions. Assume the principal Lightning payment settles successfully. Immediately afterward, the network connection disappears or the application terminates before the fee operation completes. Explain how you would design the persistent transaction state machine so that, after restart: 1. BitRelay knows the principal has already settled; 2. the principal cannot be sent twice; 3. the user correctly sees the payment as sent; 4. the unresolved fee remains independently reconcilable; and 5. duplicate callbacks, retries, or ambiguous SDK responses cannot create duplicate payments." Please do not answer only with "catch the exception and retry." We are specifically evaluating your understanding of irreversible payment settlement, persistent state, idempotency, reconciliation, and asynchronous financial transaction processing. ENGAGEMENT STRUCTURE The project will be milestone-based. M0 — Technical diligence and implementation-gap analysis M1 — Application foundation and build stabilization M2 — Wallet and key-security layer M3 — Core BitRelay payment features M4 — Payment and fee state-machine hardening M5 — Regulated-services adapter layer M6 — Security, limits, and control hardening M7 — Release candidate and final QA The first milestone will primarily involve reviewing the existing repository and technical specifications, identifying production blockers, validating the proposed Breez/Spark implementation, and producing a clear implementation plan. Architectural changes require approval before implementation. TO APPLY Please include: • Your answer to the mandatory technical question above. • Examples of production React Native apps you have built. • Specific Bitcoin / Lightning engineering experience. • Any Breez, Spark, LDK, LNURL, or embedded-wallet experience. • Examples of payment systems where you implemented idempotency or reconciliation. • Your availability. • Whether you are applying as an individual senior engineer or as part of a team. • Any immediate technical risks you see based on this description. Please do not submit a generic Web3 proposal.