Project Description
I need a blockchain developer to build a complete crypto payment infrastructure for an existing Node.js and Express web application. The system needs to generate unique HD wallet deposit addresses for each user using BIP44 derivation for Bitcoin, Ethereum, Litecoin, and Solana. When a user deposits crypto to their unique address the system must detect the transaction, verify it on-chain, credit the user's USD balance in the database, and immediately sweep the crypto to the owner's personal wallet. The system must handle ERC20 token deposits for USDT and USDC on Ethereum addresses, detect blockchain reorgs, handle Bitcoin RBF transactions, and include a gas top up bot for Ethereum sweeps. All balance updates must use atomic PostgreSQL transactions with row level locking and an immutable ledger must log every single balance change. A daily reconciliation job must verify all on-chain arrivals match balance credits. An address verification security system must re-derive every address from the master seed before any financial operation and trigger tiered security responses if any mismatch is detected. All work must be done on testnet first before mainnet. Full detailed specification documents will be provided.