Apollo Common Errors Overview Comprehensive guide to diagnosing and fixing Apollo.io API errors. Apollo uses header authentication and the base URL . Apollo distinguishes between master and standard API keys — many endpoints require master keys. Prerequisites - Valid Apollo.io API credentials - Node.js 18+ or Python 3.10+ Instructions Step 1: Identify the Error Category Step 2: Handle 401 — Invalid API Key Common 401 causes: 1. Using query parameter instead of header 2. Key was revoked or regenerated in the dashboard 3. Key has trailing whitespace (check with ) Step 3: Handle 403 — Wrong Key…