I run a fully custom PHP billing platform and I’m ready to connect it to the GST Pro REST service. The goal is to make every GST touchpoint—GSTIN checks, invoice synchronisation, e-way-bill creation and other automation—happen seamlessly inside the application. You’ll receive the official GST Pro documentation, access to a staging clone of the site, and a test API key. Your job is to wire the endpoints into our existing codebase, return clean JSON responses, and make sure data flows reliably to and from GST Pro without slowing the UI. Key deliverables • Complete REST setup: authentication, environment switching (sandbox / live) and robust error handling • Real-time GSTIN validation hooked into our customer-onboarding form • Automatic push/pull of invoice data, including status updates and reconciliation callbacks • E-way-bill generation and retrieval integrated into the dispatch module • Unit and end-to-end tests demonstrating success cases, common failures and graceful fallbacks • Concise implementation notes so my in-house team can maintain the code Acceptance criteria All listed features must function in the staging site, pass the provided test scripts, and then repeat successfully in production with real credentials. I’m available throughout the integration for questions and quick code reviews, and I can merge your pull requests rapidly to keep momentum high.