The symptom

A red console message about "No 'Access-Control-Allow-Origin' header". The request works in curl and from Postman, and fails in the browser.

What's happening

This is a browser security rule, not a bug. A page on one origin can't read a response from another origin unless that server explicitly allows it. Your API is fine. The browser is refusing to hand you the response.

Two things follow from this. The fix belongs on the server, not in your frontend. And no amount of changing your fetch call will help.

The fix

The server that receives the request must send the headers permitting your origin:

cors-fix.txt
My page at <origin> calls my API at <origin> and the browser blocks it
with a CORS error. Server stack: <stack>.

- Add the correct CORS headers on the server side.
- Allow only my specific origin, not "*" — especially if the endpoint
  uses cookies or credentials, where "*" isn't permitted anyway.
- Handle the OPTIONS preflight request. Explain what triggers a
  preflight, since some of my requests may not need one.
- Allow only the methods and headers I actually use.

Show me exactly where this goes in my code, and confirm it runs before
any authentication middleware rejects the preflight.

That last point catches many people: the preflight OPTIONS request carries no credentials, so auth middleware rejects it before your CORS headers are ever added.

What not to do

Don't set Access-Control-Allow-Origin: * on an authenticated API. It doesn't work with credentials, and where it does work you've made your API readable by every site.

Don't use a public CORS proxy. You're routing your users' data, including tokens, through a stranger's server.

Don't disable web security in your browser. It fixes your machine and nobody else's.

If you don't control the API, you can't fix CORS from the frontend. Call it from your own server instead — server-to-server requests aren't subject to this rule at all.