Tax ID Pro is an API that helps you validate tax ID numbers. I've worked on this off and on for a couple years now. I just launched a complete overhaul, re-writing the entire front-end with Next.js and back-end with FastAPI. My next project is to create an SDK for various languages to make implementation even easier.
You don't need to pay for SDK creation, OpenAPI-generator goes a long way https://github.com/OpenAPITools/openapi-generator