Working with AI APIs like OpenAI, Claude, and Gemini is powerful—but errors happen. This guide covers the most common AI API errors developers encounter in 2026 and how to resolve them quickly. HTTP Status Code Errors 401 Unauthorized What it means: Your API key is invalid, expired, or missing. Common causes: API key copied with extra whitespace Using a test key in production API key was revoked Billing issue with your provider Fix: javascript // Double-check your API key format const APIKEY = process.env.OPENAIAPI_KEY; if (!APIKEY || APIKEY === 'your-key-here') { throw new Error('API key not configured'); } 403 Forbidden What it means: You don't have permission to access this resource. Often caused by: IP restrictions enabled on your account Regional access limitations Insufficient plan tier Fix: Check your provider's dashboard for IP allowlisting or contact support. 429 Rate Limit Exceeded What it means: You've sent too many requests in a short time window.…