The CORS error that kills every developer’s first API integration — and the serverless proxy pattern that solves it permanently. If you’ve ever built something that calls an external API directly from the browser and seen this: TypeError: Failed to fetch Access to fetch at 'https://api.example.com' from origin 'https://yourapp.com' has been blocked by CORS policy Enter fullscreen mode Exit fullscreen mode This post is for you. I hit this exact wall building a live subscription dashboard on RevenueCat’s Charts API. The API works perfectly. The dashboard works perfectly. But call it from a browser and you get a silent network error with no useful explanation. Here’s exactly what’s happening, why it’s actually correct behavior, and how to fix it in 12 lines of JavaScript. What CORS Actually Is CORS stands for Cross-Origin Resource Sharing. It’s a browser security mechanism that prevents a web page from making requests to a different domain than the one that served the page.…