Preflight response is not successful

You should add the address of your requesting site URL in CORS in your Server/Backend code. Each language or framework might have their own way of adding this, try to search "[backend language] cors" (e.g. "C# cors") in google. (credits to @Gary Liu - MSFT)

You can confirm you have added correct origin by inspecting network tab in developer's console.

First select the request with method OPTIONS

Then verify the Access-Control-Allow-Origin is the same with your Origin