ERPNext-NES e-Invoice API Integration

I need a developer who can wire my existing ERPNext instance to the NES e-invoicing portal through their public APIs. The goal is to move three data groups automatically—invoice details, payment information, and full customer records—while also covering edge cases such as withholding-tax entries, refunds, and any other special scenarios the portal supports.

The workflow I have in mind is straightforward: when an invoice is issued in ERPNext it should be created instantly in NES, the corresponding payment status must stay in sync both ways, and all the tax figures have to flow through so that my statutory reports remain accurate without any manual uploads. An API-based approach is mandatory, yet I’m open to micro-services or a lightweight middleware layer if you feel that improves stability.

Deliverables
• A fully working codebase or app inside ERPNext that calls the NES REST endpoints, handles authentication tokens, retries, and error logging.
• Configuration notes and a concise setup guide so I can reproduce the integration on staging and production.
• Unit or functional tests proving that invoice creation, payment updates, and tax reporting all post successfully and receive the expected NES responses.
• Short hand-off session or video walkthrough.

I will provide sandbox credentials for both systems. Let me know your relevant ERPNext API work, approximate timeline, and any questions about the NES docs so we can get started right away.