Reverse-Engineer Marketplace Backend API

We own and operate a custom marketplace website. The frontend communicates with the backend via internal HTTP requests, but there is no documented or formal API.

We are looking for an experienced backend engineer to:

Analyze frontend network traffic
Identify and document internal requests
Implement automated messaging triggered by digital product purchases

Requirements:
Strong experience with browser DevTools & network inspection
Backend development (Python or Node.js)
Experience with authentication, tokens, CSRF

We have this tool we would like to explore:
https://docs.browser-use.com/customize/skills/basics
https://x.com/mamagnus00/status/1995600813176365393


Bonus:

Experience modernizing legacy systems
API design (REST / GraphQL)
This is for a website we own and control.