Cryptocurrency Payment Gateway Development

We are looking for a full-stack Web3 developer to complete and productionize a cryptocurrency payment gateway. The product enables merchants to accept TEXITcoin (TXC) and PUREmedal (PURE) payments, with a merchant dashboard and a customer checkout flow. The core architecture is in place; we need someone who can close gaps, fix edge cases, align frontend and backend, and prepare for deployment.

About the Project

Product: Payment gateway (branded “Kryptopay”) for TXC and PURE. Merchants get API keys, configure webhooks and wallets (HD/xpub or static addresses), and receive payments; customers are shown a payment address and real-time status until the order is confirmed and the merchant is notified via webhook.

Backend: Node.js (Express), MongoDB (Mongoose), Bitcoin-style JSON-RPC (full nodes), ZMQ (transaction notifications), HD wallet generation (BIP32/BIP84, Bech32), and AWS KMS for encrypting private keys.

Frontend: React 18, Redux Toolkit, React Router 6, Bootstrap/React-Bootstrap. Merchant dashboard (profile, balances, withdrawals, transactions) and customer checkout (address request, QR code, status polling).

Responsibilities

Complete core flows: Ensure end-to-end payment flow (address generation → payment detection → confirmation → webhook) works reliably for both TXC and PURE.

Extend real-time detection: Add PURE chain support to the ZMQ-based transaction subscriber (currently only TXC is wired).

Fix known issues: Address xpub vs seed handling (e.g. receive-only addresses and withdrawals), v1/v2 API alignment with the frontend (profile, wallets, txverif), and withdrawal error handling (e.g. check signing result before broadcast).

Improve robustness: Add tests (unit and integration where possible), improve error handling and logging, and consider webhook retries (e.g. queue + backoff).

Deployment readiness: Document and/or automate running API server, ZMQ worker, and address-refresh worker; clarify environment and node requirements.