tansahoo007/Securepay-mern-backend ? reverse-engineered prompt

Build me the backend for a PhonePe style money app.

I want users to be able to register and log in with JWT, then get a unique UPI id automatically. After login, they should be able to set up a 4 digit MPIN and use it for money transfers and bill payments. Make it so they can send money to another user using either a phone number or a UPI id, add money to their wallet for testing, and pay mock bills like mobile recharge or electricity. Keep a full transaction history for each user, including transfers, top ups, and bill payments.

Please also include a simple Swagger page so I can view and try the APIs in the browser, plus a seed script with a few demo users so I can test everything quickly. Use Node, Express, MongoDB, and keep the code beginner friendly and well commented. If you need to check any current package docs, look them up online.