Why doesn't IE 11 see or accept allow headers?

Question

Internet Explorer

Faced with the fact that when sending a request with a custom header, IE 11 gives an error:

The resource request header is not in the Access-Control-Allow-Headers.-Control-Allow-Headers list.

Although the OPTIONS request response itself shows that it is present and allowed.

In all other browsers everything works fine.

Answer 1

You have a bunch of tabs before accept, maybe that's why it breaks when parsing allowed headers.