Validate Every Webhook Signature
Never trust incoming webhook payloads automatically. If you assume every incoming notification is legitimate, attackers will eventually spoof deposit confirmations, payment notifications, settlement events, or transfer updates to trick your system into crediting fake funds. To protect your database, you must always compute the webhook signature locally and compare it directly against the provider's signature. If there is a mismatch, reject the payload immediately. Absolutely no user balance update or fund release should ever occur before that signature validation definitively succeeds.

Design for Idempotency
Networks stutter, and the internet will inevitably retry requests. Because of this, your backend must be engineered to safely handle duplicate payment notifications, settlement callbacks, wallet updates, and webhook retries without breaking a sweat. Building for idempotency simply means that processing the exact same request multiple times will only ever execute the action once. If you fail to design your system this way, a minor network hiccup is all it takes for users to get double-credited, withdrawals to duplicate, inventory to ship twice, and your entire accounting ledger to collapse.

Use Replay Attack Protection
An attacker doesn't always need to forge a new transaction to drain your treasury; sometimes they just capture a perfectly valid request and resend it over and over. To stop this, your APIs must enforce strict replay attack protection. You need to secure your endpoints by implementing a unique nonce, short request expiration windows, and strict timestamp validation on every signed request. If a request arrives stale, carries an expired payload, or features a duplicate signature you've already processed, your server must drop it instantly.

Implement Strict Rate Limiting
Rate limits exist to protect your infrastructure's stability under pressure. Every API you build or consume must enforce request throttling, burst control, strict IP limits, user-level quotas, and active anomaly detection to prevent your servers from being overwhelmed. When your system inevitably hits a ceiling and receives a 429 Too Many Requests response, it shouldn't crash or panic-spam the endpoint. You must engineer your backend to handle these constraints gracefully by utilizing exponential backoff loops, intelligent retry queues, and request batching.