How to resolve ‘preflight is invalid (redirect)’ or ‘redirect is not allowed for a preflight request’

Short answer: Make the request URL in your code isn’t missing a trailing slash. A missing-trailing-slash problem is the most-common cause of the error cited in the question. But that’s not the only cause — just the most common. Read on for more details. When you see this error, it means your code is triggering your browser … Read more

No ‘Access-Control-Allow-Origin’ header is present on the requested resource—when trying to get data from a REST API

This answer covers a lot of ground, so it’s divided into three parts: How to use a CORS proxy to get around “No Access-Control-Allow-Origin header” problems How to avoid the CORS preflight How to fix “Access-Control-Allow-Origin header must not be the wildcard” problems How to use a CORS proxy to avoid “No Access-Control-Allow-Origin header” problems … Read more