MERN Inventory Stock API Enhancement

I already have a full MERN-based clothing store in production, but the backend APIs that track inventory are still too basic. Right now each purchase simply decrements a number in MongoDB; I need a more... (Budget: ₹750 - ₹1250 INR, Jobs: AngularJS, API Development, JavaScript, MERN, MongoDB, Node.js, NoSQL Couch & Mongo, RESTful API)