Exact Same Request Returns 200 to Postman but 404 to React App

Since you have your CORS set up, all you need to do next is handle the 'preflight' OPTIONS request. You can do this using a middleware:

PreflightRequestMiddleware:

if ($request->getMethod() === $request::METHOD_OPTIONS) {    return response()->json([],204);}return $next($request);

Add the above code in the handle() method of the newly created middleware. Add the middleware in the global middleware stack.

Also, do not forget to add the OPTIONS method to Access-Control-Allow-Methods in your CORS setup.

For more options, check this out.

Answer:

Read this article. When the browser sends OPTIONS request to your application, the application has no way of handling it since you only defined a GET/POST/DELETE/PUT/PATCH route for the given endpoint.

So, in order for this route to work with preflight requests:

Route::get('/users', 'UserController@index');

it would need a corresponding OPTIONS route:

Route::options('/users', 'UserController@options');

Note: You would use a middleware to handle all OPTIONS requests in one place. If, however, you are using OPTIONS requests for other purposes - check the first link in this answer for more options.