Senior Full-Stack Developer — E-commerce Modernization

I have an existing full-stack e-commerce application that is already functional. Customers can currently browse products, add items to the cart, and complete purchases using credit cards.

I am looking for a **senior full-stack developer** to review the existing codebase, modernize several technical areas, and add cryptocurrency wallet/payment functionality.

This is **not a greenfield project**. You will be working with an existing application, so the ability to understand unfamiliar code and improve it without unnecessarily rewriting everything is very important.

### Main Requirements

The project includes:

* E-commerce storefront
* Product catalog and product details
* Shopping cart
* Checkout
* Customer accounts
* Orders
* Inventory
* Admin/dashboard functionality
* Existing credit-card payment flow

The project needs several technical improvements, including:

**1. Codebase modernization**

* Improve frontend/backend architecture where necessary
* Improve code quality and maintainability
* Improve API structure and validation
* Improve error handling
* Identify and fix technical issues
* Improve performance and reliability where appropriate

**2. Payment architecture**

The current system supports credit-card payments.

I want the payment architecture to be flexible enough to support multiple payment methods, including cryptocurrency.

**3. Cryptocurrency / Web3 integration**

Add cryptocurrency functionality using a browser wallet.

The implementation may include:

* Wallet connection
* Wallet address detection
* Network detection
* Connect/disconnect functionality
* Crypto payment initiation
* Transaction hash handling
* Backend transaction verification
* Payment status handling
* Connecting blockchain payments with existing orders
* Handling failed, pending, and successful transactions

Development should initially use a **test network/test environment**. No real cryptocurrency should be required.

### Technical Background

Strong experience with the following is preferred:

* React
* TypeScript
* Node.js
* Express
* MongoDB
* REST APIs
* E-commerce applications
* Payment integrations
* Web3/blockchain
* Ethereum/EVM
* MetaMask, Rabby, WalletConnect, or similar
* ethers.js, viem, wagmi, or similar technologies

You do not need to have experience with every technology listed, but you should be comfortable working with an existing full-stack application and integrating Web3 functionality into it.

### What I Value

I am looking for someone who:

* Can understand an unfamiliar codebase quickly
* Can debug existing software
* Makes pragmatic architectural decisions
* Understands payment security
* Understands blockchain transaction flows
* Writes maintainable TypeScript
* Can work independently
* Can use AI coding tools effectively while still understanding the code being produced

**I am not looking for a developer who simply proposes rewriting the entire application.**

The goal is to take an existing working e-commerce platform and **modernize it intelligently while adding reliable cryptocurrency functionality.**

### Proposal

Please include:

1. Your experience with React/Node.js e-commerce applications.
2. Your experience with Web3/crypto wallets.
3. Which wallet technologies you have worked with.
4. Your experience with payment integrations.
5. Your approach to adding cryptocurrency payments to an existing e-commerce application.
6. Your estimated timeline.
7. Your hourly rate or fixed-price estimate.

Please keep your proposal focused on relevant experience with **existing applications, payment systems, and Web3 integrations**.