Build Secure Crypto Payment Gateways

This skill provides expertise in cryptocurrency payment gateways, blockchain integration, and digital asset payment processing, with deep knowledge of blockchain networks, payment protocols, smart contracts, wallet integrations, and the technical architecture needed for secure, scalable crypto payment systems. Core architecture principles emphasize multi-blockchain support from the start, using a modular design with a per-chain handler (Ethereum, Bitcoin, Polygon, BSC) behind a common PaymentGateway interface that routes payments to the correct chain handler. Transaction monitoring implements robust confirmation tracking with a configurable required-confirmations threshold, polling the transaction receipt and current block number to compute confirmation count and resolving once the threshold is met.

Smart contract integration covers designing a payment contract with proper access control and event emission - a Solidity contract using OpenZeppelin's ReentrancyGuard and Ownable, tracking payments by a derived payment ID, supporting both native ETH and accepted ERC-20 tokens, and emitting a PaymentReceived event with the payer, token, amount, and order ID for off-chain reconciliation. Wallet integration patterns cover MetaMask connection with proper error handling (requesting accounts and chain ID, throwing clear errors if MetaMask isn't installed or connection fails) and network switching (requesting a chain switch via wallet_switchEthereumChain, falling back to adding the network if it isn't yet configured in the wallet).

Price feed integration covers real-time price updates from reliable oracles - a PriceFeedManager fetching token-to-fiat conversion rates from CoinGecko's API (with Chainlink contract addresses as an on-chain alternative) to ensure accurate payment amount conversion at the time of transaction.

Use this skill when building a cryptocurrency payment gateway that needs multi-chain support, on-chain payment contracts, wallet connection, transaction confirmation monitoring, and accurate price conversion. It is well suited to e-commerce or SaaS platforms adding crypto as a payment option alongside traditional methods. It is not meant for pure DeFi protocol development with no payment-gateway use case, or for a single-chain, single-token integration where the full multi-chain architecture is unnecessary overhead.

Input: the target blockchain networks, accepted tokens, and required confirmation thresholds.

Output: a multi-chain payment gateway architecture, a payment smart contract, wallet connection code, and price feed integration. Example payment contract event:

event PaymentReceived(
    bytes32 indexed paymentId,
    address indexed payer,
    address token,
    uint256 amount,
    string orderId
);

Works with Ethereum, Bitcoin, Polygon, and BSC networks, OpenZeppelin contract libraries, MetaMask wallet connection, and CoinGecko/Chainlink price feeds.

Blockchain and payments engineers building a cryptocurrency payment gateway, and platforms adding multi-chain crypto payment support alongside traditional payment methods.