46. Signing & Verifying Blockchain Transactions

When a Laravel backend needs to submit transactions (e.g., minting an NFT after a payment), it typically constructs the transaction payload, signs it with a securely stored private key (often via a KMS or hardware wallet integration rather than plaintext in .env), and broadcasts it via eth_sendRawTransaction. Nonce management is critical: concurrent requests using the same account must serialize nonce assignment, often via a database lock or cache-based counter, to avoid 'nonce too low' errors. Gas price/fee estimation should call eth_gasPrice or eth_feeHistory before submission to avoid stuck or overpriced transactions.