Getting CORS error when Oauth 2.0 /token endpoint is called

Hi, We have a eloqua app installed. We are using Oauth 2.0. Our app build is deployed on our server. When user authorizes the when the app is clicked in Eloqua, we try to hit the token endpoint to get the access_tokens and refresh_token so that we can store them. But we see following error in the browser console.

Access to XMLHttpRequest at 'https://login.eloqua.com/auth/oauth2/token?grant_type=authorization_code&code=OTUwMzA0NDUwOjFFQjNTdn52RDdVMnZiYTZmNTduSjVKSy1RcWppbWduQ1JQdDcyUnoyTXdGZ2xQOXJabE5kdHduUEo5TDNtY2ZQRjladUxQVXdlcEYya1Q0RnVTaUVaaXdsdmxMOHRDd2ZSTXg=&redirect_uri=https://abc.xyz.com/eloqua-app' from origin 'https://abc.xyz.com'