Custom Crypto Payment Gateway Integration

I’m building a small-scale payment gateway that lets shoppers on my Next.js e-commerce site pay with TRX, Ethereum, BTC, XMR, and LTC. The focus is on a clean, dependable setup rather than heavy, enterprise-level security; standard encryption, confirmation checks, and basic anti-fraud routines will be enough for this first release. The gateway must handle both one-time and recurring payments. I’ll need simple merchant controls—think invoice generation, transaction status, and refund trigger—plus a lightweight REST or GraphQL API so my front-end can display QR codes, wallet addresses, and live confirmation counts without page reloads. Because I’m turning this into a standalone service for my own products, the codebase should be modular: a core processing service (Node or Go preferred, but I’m open) and a ready-to-drop-in Next.js component or hook set. Clean dependency management, thorough README docs, and concise comments are essential so I can extend the system later. I’ll review by running the script on testnets or small live amounts; successful confirmations and subscription renewals will mark acceptance. If you’ve built similar gateways or have code snippets demonstrating multi-coin handling, that will speed selection.