Jewellery E-Invoice & E-Way API -- 2

I’m building a jewellery–specific billing system and now require a clean, well-documented REST API to plug into it. The service must let my app:

• Accept either XML or JSON payloads and return a complete e-invoice response that includes the government-issued ARN.
• Use the same source data to raise an e-way bill.
• Fetch registered-owner details instantly when I supply a GST number.

An API-Key header will secure every call; no other auth flow is necessary. You are free to choose the most suitable language and framework, as long as the endpoints remain lean, fast and easy to containerise.

Deliverables
1. Source code with clear folder structure and comments.
2. Three working endpoints (/einvoice/getGSTOwnerDetails) returning validated responses.
3. Postman or Swagger collection showing sample XML and JSON calls.
4. Setup guide plus quick README outlining how to configure the API-Key and run the service in local and staging environments.

I will test by posting my own XML and JSON jewellery-billing files; the call should reply with the correct ARN or e-way number, or the exact GST profile. Once those checks pass, the job is complete.

we will provide sml or json of a sales details from our jewellery software